diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/AddTimestampAttribute.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/AddTimestampAttribute.java
index 0ecafc82f90b..2fd3032c0da1 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/AddTimestampAttribute.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/AddTimestampAttribute.java
@@ -18,6 +18,7 @@
 package org.apache.beam.sdk.io.gcp.pubsub;
 
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubMessageToRow.TIMESTAMP_FIELD;
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
 
 import org.apache.beam.sdk.schemas.transforms.DropFields;
 import org.apache.beam.sdk.transforms.PTransform;
@@ -31,9 +32,6 @@
  * Adds a timestamp attribute if desired and filters it out of the underlying row if no timestamp
  * attribute exists.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 class AddTimestampAttribute extends PTransform<PCollection<Row>, PCollection<Row>> {
   private static final Logger LOG = LoggerFactory.getLogger(AddTimestampAttribute.class);
   private final boolean useTimestampAttribute;
@@ -48,7 +46,14 @@ public PCollection<Row> expand(PCollection<Row> input) {
     // element's event time. PubSubIO will populate the attribute from there.
     PCollection<Row> withTimestamp =
         useTimestampAttribute
-            ? input.apply(WithTimestamps.of((row) -> row.getDateTime(TIMESTAMP_FIELD).toInstant()))
+            ? input.apply(
+                WithTimestamps.of(
+                    (row) ->
+                        checkArgumentNotNull(
+                                row.getDateTime(TIMESTAMP_FIELD),
+                                "Field '%s' must be present and non-null in the input row when writing to PubSub with a timestamp attribute.",
+                                TIMESTAMP_FIELD)
+                            .toInstant()))
             : input;
 
     PCollection<Row> rows;
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/ExternalWrite.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/ExternalWrite.java
index 23b14b68a08b..3bcc83aed78b 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/ExternalWrite.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/ExternalWrite.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+
 import com.google.auto.service.AutoService;
 import java.util.Map;
 import org.apache.beam.sdk.expansion.ExternalTransformRegistrar;
@@ -35,9 +37,6 @@
 
 /** Exposes {@link PubsubIO.Write} as an external transform for cross-language usage. */
 @AutoService(ExternalTransformRegistrar.class)
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public final class ExternalWrite implements ExternalTransformRegistrar {
   public ExternalWrite() {}
 
@@ -50,7 +49,7 @@ public ExternalWrite() {}
 
   /** Parameters class to expose the transform to an external SDK. */
   public static class Configuration {
-    private String topic;
+    private @Nullable String topic;
     private @Nullable String idAttribute;
     private @Nullable String timestampAttribute;
     private boolean publishWithOrderingKey = false;
@@ -80,8 +79,9 @@ public WriteBuilder() {}
     public PTransform<PCollection<byte[]>, PDone> buildExternal(Configuration config) {
       PubsubIO.Write.Builder<byte[]> writeBuilder =
           PubsubIO.Write.newBuilder(new ParsePubsubMessageProtoAsPayloadFromWindowedValue());
-      if (config.topic != null) {
-        StaticValueProvider<String> topic = StaticValueProvider.of(config.topic);
+      String topicStr = config.topic;
+      if (topicStr != null) {
+        StaticValueProvider<String> topic = StaticValueProvider.of(topicStr);
         writeBuilder.setTopicProvider(NestedValueProvider.of(topic, PubsubTopic::fromPath));
       }
       if (config.idAttribute != null) {
@@ -102,7 +102,8 @@ public static class ParsePubsubMessageProtoAsPayloadFromWindowedValue
 
     @Override
     public PubsubMessage apply(ValueInSingleWindow<byte[]> input) {
-      return INNER.apply(input.getValue());
+      return INNER.apply(
+          checkArgumentNotNull(input.getValue(), "Windowed value input cannot be null"));
     }
   }
 }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/NestedRowToMessage.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/NestedRowToMessage.java
index 9c56410cda6b..50325f7b39e2 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/NestedRowToMessage.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/NestedRowToMessage.java
@@ -22,6 +22,7 @@
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubSchemaIOProvider.ATTRIBUTE_ARRAY_FIELD_TYPE;
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubSchemaIOProvider.ATTRIBUTE_MAP_FIELD_TYPE;
 import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
 
 import java.util.Collection;
@@ -34,16 +35,17 @@
 import org.apache.beam.sdk.transforms.SimpleFunction;
 import org.apache.beam.sdk.values.Row;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableMap;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 class NestedRowToMessage extends SimpleFunction<Row, PubsubMessage> {
   private static final long serialVersionUID = 65176815766314684L;
 
-  private final PayloadSerializer serializer;
+  private final @Nullable PayloadSerializer serializer;
   private final SerializableFunction<Row, Map<String, String>> attributesExtractor;
   private final SerializableFunction<Row, byte[]> payloadExtractor;
 
   @SuppressWarnings("methodref.receiver.bound")
-  NestedRowToMessage(PayloadSerializer serializer, Schema schema) {
+  NestedRowToMessage(@Nullable PayloadSerializer serializer, Schema schema) {
     this.serializer = serializer;
     if (schema.getField(ATTRIBUTES_FIELD).getType().equals(ATTRIBUTE_MAP_FIELD_TYPE)) {
       attributesExtractor = NestedRowToMessage::getAttributesFromMap;
@@ -81,7 +83,7 @@ private static byte[] getPayloadFromBytes(Row row) {
   }
 
   private byte[] getPayloadFromNested(Row row) {
-    return serializer.serialize(checkArgumentNotNull(row.getRow(PAYLOAD_FIELD)));
+    return checkStateNotNull(serializer).serialize(checkArgumentNotNull(row.getRow(PAYLOAD_FIELD)));
   }
 
   @Override
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubSubPayloadTranslation.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubSubPayloadTranslation.java
index b77928bd957e..eec590a480f7 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubSubPayloadTranslation.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubSubPayloadTranslation.java
@@ -19,6 +19,7 @@
 
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubIO.ENABLE_CUSTOM_PUBSUB_SINK;
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubIO.ENABLE_CUSTOM_PUBSUB_SOURCE;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 
 import com.google.auto.service.AutoService;
 import java.util.Collections;
@@ -37,16 +38,13 @@
 import org.apache.beam.sdk.options.ValueProvider.NestedValueProvider;
 import org.apache.beam.sdk.runners.AppliedPTransform;
 import org.apache.beam.sdk.transforms.PTransform;
-import org.apache.beam.sdk.util.Preconditions;
 import org.apache.beam.sdk.util.construction.PTransformTranslation;
 import org.apache.beam.sdk.util.construction.PTransformTranslation.TransformPayloadTranslator;
 import org.apache.beam.sdk.util.construction.SdkComponents;
 import org.apache.beam.sdk.util.construction.TransformPayloadTranslatorRegistrar;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableMap;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 /**
  * Utility methods for translating a {@link Unbounded} which reads from {@link
  * PubsubUnboundedSource} to {@link RunnerApi} representations.
@@ -61,7 +59,7 @@ public String getUrn() {
     }
 
     @Override
-    public RunnerApi.FunctionSpec translate(
+    public RunnerApi.@Nullable FunctionSpec translate(
         AppliedPTransform<?, ?, Unbounded<?>> transform, SdkComponents components) {
       if (ExperimentalOptions.hasExperiment(
           transform.getPipeline().getOptions(), ENABLE_CUSTOM_PUBSUB_SOURCE)) {
@@ -93,11 +91,13 @@ public RunnerApi.FunctionSpec translate(
         }
       }
 
-      if (pubsubUnboundedSource.getTimestampAttribute() != null) {
-        payloadBuilder.setTimestampAttribute(pubsubUnboundedSource.getTimestampAttribute());
+      String timestampAttribute = pubsubUnboundedSource.getTimestampAttribute();
+      if (timestampAttribute != null) {
+        payloadBuilder.setTimestampAttribute(timestampAttribute);
       }
-      if (pubsubUnboundedSource.getIdAttribute() != null) {
-        payloadBuilder.setIdAttribute(pubsubUnboundedSource.getIdAttribute());
+      String idAttribute = pubsubUnboundedSource.getIdAttribute();
+      if (idAttribute != null) {
+        payloadBuilder.setIdAttribute(idAttribute);
       }
       payloadBuilder.setWithAttributes(
           pubsubUnboundedSource.getNeedsAttributes() || pubsubUnboundedSource.getNeedsMessageId());
@@ -116,7 +116,7 @@ public String getUrn() {
     }
 
     @Override
-    public RunnerApi.FunctionSpec translate(
+    public RunnerApi.@Nullable FunctionSpec translate(
         AppliedPTransform<?, ?, PubsubUnboundedSink.PubsubSink> transform,
         SdkComponents components) {
       if (ExperimentalOptions.hasExperiment(
@@ -125,19 +125,20 @@ public RunnerApi.FunctionSpec translate(
       }
       PubSubWritePayload.Builder payloadBuilder = PubSubWritePayload.newBuilder();
       ValueProvider<TopicPath> topicProvider =
-          Preconditions.checkStateNotNull(transform.getTransform().outer.getTopicProvider());
+          checkStateNotNull(transform.getTransform().outer.getTopicProvider());
       if (topicProvider.isAccessible()) {
         payloadBuilder.setTopic(topicProvider.get().getFullPath());
       } else {
         payloadBuilder.setTopicRuntimeOverridden(
             ((NestedValueProvider) topicProvider).propertyName());
       }
-      if (transform.getTransform().outer.getTimestampAttribute() != null) {
-        payloadBuilder.setTimestampAttribute(
-            transform.getTransform().outer.getTimestampAttribute());
+      String timestampAttribute = transform.getTransform().outer.getTimestampAttribute();
+      if (timestampAttribute != null) {
+        payloadBuilder.setTimestampAttribute(timestampAttribute);
       }
-      if (transform.getTransform().outer.getIdAttribute() != null) {
-        payloadBuilder.setIdAttribute(transform.getTransform().outer.getIdAttribute());
+      String idAttribute = transform.getTransform().outer.getIdAttribute();
+      if (idAttribute != null) {
+        payloadBuilder.setIdAttribute(idAttribute);
       }
       return FunctionSpec.newBuilder()
           .setUrn(getUrn(transform.getTransform()))
@@ -154,7 +155,7 @@ public String getUrn() {
     }
 
     @Override
-    public RunnerApi.FunctionSpec translate(
+    public RunnerApi.@Nullable FunctionSpec translate(
         AppliedPTransform<?, ?, PubsubUnboundedSink.PubsubDynamicSink> transform,
         SdkComponents components) {
       if (ExperimentalOptions.hasExperiment(
@@ -162,12 +163,13 @@ public RunnerApi.FunctionSpec translate(
         return null;
       }
       PubSubWritePayload.Builder payloadBuilder = PubSubWritePayload.newBuilder();
-      if (transform.getTransform().outer.getTimestampAttribute() != null) {
-        payloadBuilder.setTimestampAttribute(
-            transform.getTransform().outer.getTimestampAttribute());
+      String timestampAttribute = transform.getTransform().outer.getTimestampAttribute();
+      if (timestampAttribute != null) {
+        payloadBuilder.setTimestampAttribute(timestampAttribute);
       }
-      if (transform.getTransform().outer.getIdAttribute() != null) {
-        payloadBuilder.setIdAttribute(transform.getTransform().outer.getIdAttribute());
+      String idAttribute = transform.getTransform().outer.getIdAttribute();
+      if (idAttribute != null) {
+        payloadBuilder.setIdAttribute(idAttribute);
       }
       return FunctionSpec.newBuilder()
           .setUrn(getUrn(transform.getTransform()))
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubClient.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubClient.java
index 333497462177..3f4d5765b66c 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubClient.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubClient.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
@@ -40,13 +42,11 @@
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableMap;
 import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.dataflow.qual.Pure;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /** An (abstract) helper class for talking to Pubsub via an underlying transport. */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public abstract class PubsubClient implements Closeable {
   private static final Logger LOG = LoggerFactory.getLogger(PubsubClient.class);
   private static final Map<String, SerializableFunction<String, Schema>>
@@ -82,7 +82,7 @@ PubsubClient newClient(
    * Return timestamp as ms-since-unix-epoch corresponding to {@code timestamp}. Throw {@link
    * IllegalArgumentException} if timestamp cannot be recognized.
    */
-  protected static Long parseTimestampAsMsSinceEpoch(String timestamp) {
+  protected static long parseTimestampAsMsSinceEpoch(String timestamp) {
     if (timestamp.isEmpty()) {
       throw new IllegalArgumentException("Empty timestamp.");
     }
@@ -113,17 +113,12 @@ protected static long extractTimestampAttribute(
       String timestampAttribute, @Nullable Map<String, String> attributes) {
     Preconditions.checkState(!timestampAttribute.isEmpty());
     String value = attributes == null ? null : attributes.get(timestampAttribute);
-    checkArgument(
-        value != null,
-        "PubSub message is missing a value for timestamp attribute %s",
-        timestampAttribute);
-    Long timestampMsSinceEpoch = parseTimestampAsMsSinceEpoch(value);
-    checkArgument(
-        timestampMsSinceEpoch != null,
-        "Cannot interpret value of attribute %s as timestamp: %s",
-        timestampAttribute,
-        value);
-    return timestampMsSinceEpoch;
+    String nonNullValue =
+        checkArgumentNotNull(
+            value,
+            "PubSub message is missing a value for timestamp attribute %s",
+            timestampAttribute);
+    return parseTimestampAsMsSinceEpoch(nonNullValue);
   }
 
   /** Path representing a cloud project id. */
@@ -386,17 +381,21 @@ public static TopicPath topicPathFromName(String projectId, String topicName) {
   public abstract static class OutgoingMessage implements Serializable {
 
     /** Underlying Message. May not have publish timestamp set. */
+    @Pure
     public abstract PubsubMessage getMessage();
 
     /** Timestamp for element (ms since epoch). */
+    @Pure
     public abstract long getTimestampMsSinceEpoch();
 
     /**
      * If using an id attribute, the record id to associate with this record's metadata so the
      * receiver can reject duplicates. Otherwise {@literal null}.
      */
+    @Pure
     public abstract @Nullable String recordId();
 
+    @Pure
     public abstract @Nullable String topic();
 
     public static OutgoingMessage of(
@@ -415,11 +414,13 @@ public static OutgoingMessage of(
         @Nullable String topic) {
       PubsubMessage.Builder builder =
           PubsubMessage.newBuilder().setData(ByteString.copyFrom(message.getPayload()));
-      if (message.getAttributeMap() != null) {
-        builder.putAllAttributes(message.getAttributeMap());
+      Map<String, String> attributeMap = message.getAttributeMap();
+      if (attributeMap != null) {
+        builder.putAllAttributes(attributeMap);
       }
-      if (message.getOrderingKey() != null) {
-        builder.setOrderingKey(message.getOrderingKey());
+      String orderingKey = message.getOrderingKey();
+      if (orderingKey != null) {
+        builder.setOrderingKey(orderingKey);
       }
       return of(builder.build(), timestampMsSinceEpoch, recordId, topic);
     }
@@ -435,21 +436,23 @@ public static OutgoingMessage of(
   public abstract static class IncomingMessage implements Serializable {
 
     /** Underlying Message. */
+    @Pure
     public abstract PubsubMessage message();
 
-    /**
-     * Timestamp for element (ms since epoch). Either Pubsub's processing time, or the custom
-     * timestamp associated with the message.
-     */
+    /** Either Pubsub's processing time, or the custom timestamp associated with the message. */
+    @Pure
     public abstract long timestampMsSinceEpoch();
 
     /** Timestamp (in system time) at which we requested the message (ms since epoch). */
+    @Pure
     public abstract long requestTimeMsSinceEpoch();
 
     /** Id to pass back to Pubsub to acknowledge receipt of this message. */
+    @Pure
     public abstract String ackId();
 
     /** Id to pass to the runner to distinguish this message from all others. */
+    @Pure
     public abstract String recordId();
 
     public static IncomingMessage of(
@@ -554,7 +557,7 @@ public abstract void createSchema(
   public abstract void deleteSchema(SchemaPath schemaPath) throws IOException;
 
   /** Return {@link SchemaPath} from {@link TopicPath} if exists. */
-  public abstract SchemaPath getSchemaPath(TopicPath topicPath) throws IOException;
+  public abstract @Nullable SchemaPath getSchemaPath(TopicPath topicPath) throws IOException;
 
   /** Return a Beam {@link Schema} from the Pub/Sub schema resource, if exists. */
   public abstract Schema getSchema(SchemaPath schemaPath) throws IOException;
@@ -567,8 +570,10 @@ static Schema fromPubsubSchema(com.google.api.services.pubsub.model.Schema pubsu
               "Pub/Sub schema type %s is not supported at this time", pubsubSchema.getType()));
     }
     SerializableFunction<String, Schema> definitionToSchemaFn =
-        schemaTypeToConversionFnMap.get(pubsubSchema.getType());
-    return definitionToSchemaFn.apply(pubsubSchema.getDefinition());
+        checkStateNotNull(schemaTypeToConversionFnMap.get(pubsubSchema.getType()));
+    String definition =
+        checkNotNull(pubsubSchema.getDefinition(), "Pub/Sub schema definition is null");
+    return definitionToSchemaFn.apply(definition);
   }
 
   /** Convert a {@link com.google.pubsub.v1.Schema} to a Beam {@link Schema}. */
@@ -579,7 +584,7 @@ static Schema fromPubsubSchema(com.google.pubsub.v1.Schema pubsubSchema) {
           String.format("Pub/Sub schema type %s is not supported at this time", typeName));
     }
     SerializableFunction<String, Schema> definitionToSchemaFn =
-        schemaTypeToConversionFnMap.get(typeName);
+        checkStateNotNull(schemaTypeToConversionFnMap.get(typeName));
     return definitionToSchemaFn.apply(pubsubSchema.getDefinition());
   }
 
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubGrpcClient.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubGrpcClient.java
index 7fb30a1099aa..42fb80b6b42b 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubGrpcClient.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubGrpcClient.java
@@ -17,7 +17,7 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
-import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 
 import com.google.auth.Credentials;
 import com.google.protobuf.Timestamp;
@@ -67,20 +67,17 @@
 import org.apache.beam.sdk.schemas.Schema;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.annotations.VisibleForTesting;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.MoreObjects;
-import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Strings;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.util.concurrent.ThreadFactoryBuilder;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /** A helper class for talking to Pubsub via grpc. */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubGrpcClient extends PubsubClient {
   private static final int LIST_BATCH_SIZE = 1000;
 
   private static final int DEFAULT_TIMEOUT_S = 60;
 
+  @SuppressWarnings("nullness") // netty requires ciphers(null) but is not annotated
   private static ManagedChannel channelForRootUrl(String urlString) throws IOException {
     String format = PubsubOptions.targetForRootUrl(urlString);
 
@@ -104,7 +101,7 @@ public PubsubClient newClient(
         @Nullable String timestampAttribute,
         @Nullable String idAttribute,
         PubsubOptions options,
-        String rootUrlOverride)
+        @Nullable String rootUrlOverride)
         throws IOException {
       return new PubsubGrpcClient(
           timestampAttribute,
@@ -144,9 +141,9 @@ public String getKind() {
   /** Cached stubs, or null if not cached. */
   private PublisherGrpc.@Nullable PublisherBlockingStub cachedPublisherStub;
 
-  private SubscriberGrpc.SubscriberBlockingStub cachedSubscriberStub;
+  private SubscriberGrpc.@Nullable SubscriberBlockingStub cachedSubscriberStub;
 
-  private SchemaServiceGrpc.SchemaServiceBlockingStub cachedSchemaServiceStub;
+  private SchemaServiceGrpc.@Nullable SchemaServiceBlockingStub cachedSchemaServiceStub;
 
   @VisibleForTesting
   PubsubGrpcClient(
@@ -189,7 +186,8 @@ public void close() {
 
   /** Return channel with interceptor for returning credentials. */
   private Channel newChannel() throws IOException {
-    checkState(publisherChannel != null, "PubsubGrpcClient has been closed");
+    ManagedChannel channel =
+        checkStateNotNull(publisherChannel, "PubsubGrpcClient has been closed");
     ClientAuthInterceptor interceptor =
         new ClientAuthInterceptor(
             credentials,
@@ -198,7 +196,7 @@ private Channel newChannel() throws IOException {
                     .setDaemon(true)
                     .setNameFormat("PubsubGrpcClient-thread")
                     .build()));
-    return ClientInterceptors.intercept(publisherChannel, interceptor);
+    return ClientInterceptors.intercept(channel, interceptor);
   }
 
   /** Return a stub for making a publish request with a timeout. */
@@ -237,8 +235,9 @@ public int publish(TopicPath topic, List<OutgoingMessage> outgoingMessages) thro
             timestampAttribute, String.valueOf(outgoingMessage.getTimestampMsSinceEpoch()));
       }
 
-      if (idAttribute != null && !Strings.isNullOrEmpty(outgoingMessage.recordId())) {
-        message.putAttributes(idAttribute, outgoingMessage.recordId());
+      String recordId = outgoingMessage.recordId();
+      if (idAttribute != null && recordId != null && !recordId.isEmpty()) {
+        message.putAttributes(idAttribute, recordId);
       }
 
       request.addMessages(message);
@@ -267,12 +266,18 @@ public List<IncomingMessage> pull(
     }
     List<IncomingMessage> incomingMessages = new ArrayList<>(response.getReceivedMessagesCount());
     for (ReceivedMessage message : response.getReceivedMessagesList()) {
+      if (!message.hasMessage()) {
+        continue;
+      }
       PubsubMessage pubsubMessage = message.getMessage();
       Map<String, String> attributes = pubsubMessage.getAttributes();
 
       // Timestamp.
       long timestampMsSinceEpoch;
-      if (Strings.isNullOrEmpty(timestampAttribute)) {
+      if (timestampAttribute == null || timestampAttribute.isEmpty()) {
+        if (!pubsubMessage.hasPublishTime()) {
+          throw new IllegalStateException("Received message missing publishTime");
+        }
         Timestamp timestampProto = pubsubMessage.getPublishTime();
         timestampMsSinceEpoch =
             timestampProto.getSeconds() * 1000 + timestampProto.getNanos() / 1000L / 1000L;
@@ -282,14 +287,16 @@ public List<IncomingMessage> pull(
 
       // Ack id.
       String ackId = message.getAckId();
-      checkState(!Strings.isNullOrEmpty(ackId));
+      if (ackId.isEmpty()) {
+        throw new IllegalStateException("Received message missing ackId");
+      }
 
       // Record id, if any.
-      @Nullable String recordId = null;
+      String recordId = null;
       if (idAttribute != null) {
         recordId = attributes.get(idAttribute);
       }
-      if (Strings.isNullOrEmpty(recordId)) {
+      if (recordId == null || recordId.isEmpty()) {
         // Fall back to the Pubsub provided message id.
         recordId = pubsubMessage.getMessageId();
       }
@@ -475,15 +482,15 @@ public void deleteSchema(SchemaPath schemaPath) throws IOException {
 
   /** Return {@link SchemaPath} from {@link TopicPath} if exists. */
   @Override
-  public SchemaPath getSchemaPath(TopicPath topicPath) throws IOException {
+  public @Nullable SchemaPath getSchemaPath(TopicPath topicPath) throws IOException {
     GetTopicRequest request = GetTopicRequest.newBuilder().setTopic(topicPath.getPath()).build();
     Topic topic = publisherStub().getTopic(request);
-    SchemaSettings schemaSettings = topic.getSchemaSettings();
-    if (schemaSettings.getSchema().isEmpty()) {
+    if (!topic.hasSchemaSettings()) {
       return null;
     }
+    SchemaSettings schemaSettings = topic.getSchemaSettings();
     String schemaPath = schemaSettings.getSchema();
-    if (schemaPath.equals(SchemaPath.DELETED_SCHEMA_PATH)) {
+    if (schemaPath.isEmpty() || schemaPath.equals(SchemaPath.DELETED_SCHEMA_PATH)) {
       return null;
     }
     return PubsubClient.schemaPathFromPath(schemaPath);
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubIO.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubIO.java
index 57005745044b..ee4e283cc2f2 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubIO.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubIO.java
@@ -18,6 +18,8 @@
 package org.apache.beam.sdk.io.gcp.pubsub;
 
 import static org.apache.beam.sdk.transforms.errorhandling.BadRecordRouter.BAD_RECORD_TAG;
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
 
 import com.google.api.client.util.Clock;
@@ -71,7 +73,6 @@
 import org.apache.beam.sdk.transforms.errorhandling.ErrorHandler.DefaultErrorHandler;
 import org.apache.beam.sdk.transforms.windowing.AfterWatermark;
 import org.apache.beam.sdk.util.CoderUtils;
-import org.apache.beam.sdk.util.Preconditions;
 import org.apache.beam.sdk.values.EncodableThrowable;
 import org.apache.beam.sdk.values.KV;
 import org.apache.beam.sdk.values.PBegin;
@@ -112,20 +113,21 @@
  * <h3>Updates to the I/O connector code</h3>
  *
  * For any significant updates to this I/O connector, please consider involving corresponding code
- * reviewers mentioned <a
- * href="https://github.com/apache/beam/blob/master/sdks/java/io/google-cloud-platform/OWNERS">
- * here</a>.
+ * reviewers mentioned <a href=
+ * "https://github.com/apache/beam/blob/master/sdks/java/io/google-cloud-platform/OWNERS"> here</a>.
  *
  * <h3>Example PubsubIO read usage</h3>
  *
  * <pre>{@code
- * // Read from a specific topic; a subscription will be created at pipeline start time.
+ * // Read from a specific topic; a subscription will be created at pipeline
+ * // start time.
  * PCollection<PubsubMessage> messages = PubsubIO.readMessages().fromTopic(topic);
  *
  * // Read from a subscription.
  * PCollection<PubsubMessage> messages = PubsubIO.readMessages().fromSubscription(subscription);
  *
- * // Read messages including attributes. All PubSub attributes will be included in the PubsubMessage.
+ * // Read messages including attributes. All PubSub attributes will be included
+ * // in the PubsubMessage.
  * PCollection<PubsubMessage> messages = PubsubIO.readMessagesWithAttributes().fromTopic(topic);
  *
  * // Examples of reading different types from PubSub.
@@ -161,10 +163,11 @@
  * topic and writing using the {@link PubsubIO#writeMessagesDynamic()} method. For example:
  *
  * <pre>{@code
- * events.apply(MapElements.into(new TypeDescriptor<PubsubMessage>() {})
- *                         .via(e -> new PubsubMessage(
- *                             e.toByteString(), Collections.emptyMap()).withTopic(e.getCountry())))
- * .apply(PubsubIO.writeMessagesDynamic());
+ * events.apply(MapElements.into(new TypeDescriptor<PubsubMessage>() {
+ * })
+ *     .via(e -> new PubsubMessage(
+ *         e.toByteString(), Collections.emptyMap()).withTopic(e.getCountry())))
+ *     .apply(PubsubIO.writeMessagesDynamic());
  * }</pre>
  *
  * <h3>Custom timestamps</h3>
@@ -175,9 +178,6 @@
  * to be used, that timestamp must be published in a PubSub attribute and specified using {@link
  * PubsubIO.Read#withTimestampAttribute}. See the Javadoc for that method for the timestamp format.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubIO {
 
   private static final Logger LOG = LoggerFactory.getLogger(PubsubIO.class);
@@ -251,9 +251,9 @@ private static void validatePubsubName(String name) {
   /** Populate common {@link DisplayData} between Pubsub source and sink. */
   private static void populateCommonDisplayData(
       DisplayData.Builder builder,
-      String timestampAttribute,
-      String idAttribute,
-      ValueProvider<PubsubTopic> topic) {
+      @Nullable String timestampAttribute,
+      @Nullable String idAttribute,
+      @Nullable ValueProvider<PubsubTopic> topic) {
     builder
         .addIfNotNull(
             DisplayData.item("timestampAttribute", timestampAttribute)
@@ -324,6 +324,13 @@ public static PubsubSubscription fromPath(String path) {
         subscriptionName = match.group(2);
       }
 
+      projectName =
+          checkArgumentNotNull(
+              projectName, "Invalid path: project name must be non-null: %s", path);
+      subscriptionName =
+          checkArgumentNotNull(
+              subscriptionName, "Invalid path: subscription name must be non-null: %s", path);
+
       validateProjectName(projectName);
       validatePubsubName(subscriptionName);
       return new PubsubSubscription(PubsubSubscription.Type.NORMAL, projectName, subscriptionName);
@@ -399,7 +406,7 @@ public TopicPath apply(PubsubTopic from) {
   /** Class representing a Cloud Pub/Sub Topic. */
   public static class PubsubTopic implements Serializable {
     @Override
-    public boolean equals(Object o) {
+    public boolean equals(@Nullable Object o) {
       if (this == o) {
         return true;
       }
@@ -470,6 +477,12 @@ public static PubsubTopic fromPath(String path) {
         topicName = match.group(2);
       }
 
+      projectName =
+          checkArgumentNotNull(
+              projectName, "Invalid path: project name must be non-null: %s", path);
+      topicName =
+          checkArgumentNotNull(topicName, "Invalid path: topic name must be non-null: %s", path);
+
       validateProjectName(projectName);
       validatePubsubName(topicName);
       return new PubsubTopic(PubsubTopic.Type.NORMAL, projectName, topicName);
@@ -604,7 +617,8 @@ public static Read<String> readStrings() {
    */
   public static <T extends Message> Read<T> readProtos(Class<T> messageClass) {
     // TODO: Stop using ProtoCoder and instead parse the payload directly.
-    // We should not be relying on the fact that ProtoCoder's wire format is identical to
+    // We should not be relying on the fact that ProtoCoder's wire format is
+    // identical to
     // the protobuf wire format, as the wire format is not part of a coder's API.
     ProtoCoder<T> coder = ProtoCoder.of(messageClass);
     return Read.newBuilder(parsePayloadUsingCoder(coder)).setCoder(coder).build();
@@ -662,7 +676,8 @@ public static Read<DynamicMessage> readProtoDynamicMessages(Descriptor descripto
    */
   public static <T> Read<T> readAvros(Class<T> clazz) {
     // TODO: Stop using AvroCoder and instead parse the payload directly.
-    // We should not be relying on the fact that AvroCoder's wire format is identical to
+    // We should not be relying on the fact that AvroCoder's wire format is
+    // identical to
     // the Avro wire format, as the wire format is not part of a coder's API.
     AvroCoder<T> coder = AvroCoder.of(clazz);
     return Read.newBuilder(parsePayloadUsingCoder(coder)).setCoder(coder).build();
@@ -698,6 +713,10 @@ public static <T> Read<T> readMessagesWithAttributesWithCoderAndParseFn(
   public static Read<GenericRecord> readAvroGenericRecords(org.apache.avro.Schema avroSchema) {
     AvroCoder<GenericRecord> coder = AvroCoder.of(avroSchema);
     Schema schema = AvroUtils.getSchema(GenericRecord.class, avroSchema);
+    if (schema == null) {
+      throw new IllegalArgumentException(
+          "Could not infer Beam schema from Avro schema: " + avroSchema);
+    }
     return Read.newBuilder(parsePayloadUsingCoder(coder))
         .setCoder(
             SchemaCoder.of(
@@ -722,6 +741,9 @@ public static <T> Read<T> readAvrosWithBeamSchema(Class<T> clazz) {
     AvroCoder<T> coder = AvroCoder.of(clazz);
     org.apache.avro.Schema avroSchema = coder.getSchema();
     Schema schema = AvroUtils.getSchema(clazz, avroSchema);
+    if (schema == null) {
+      throw new IllegalArgumentException("Could not infer Beam schema for class: " + clazz);
+    }
     return Read.newBuilder(parsePayloadUsingCoder(coder))
         .setCoder(
             SchemaCoder.of(
@@ -773,7 +795,8 @@ public static Write<String> writeStrings() {
    * Google Cloud Pub/Sub stream.
    */
   public static <T extends Message> Write<T> writeProtos(Class<T> messageClass) {
-    // TODO: Like in readProtos(), stop using ProtoCoder and instead format the payload directly.
+    // TODO: Like in readProtos(), stop using ProtoCoder and instead format the
+    // payload directly.
     return Write.newBuilder(formatPayloadUsingCoder(ProtoCoder.of(messageClass)))
         .setDynamicDestinations(false)
         .build();
@@ -786,7 +809,8 @@ public static <T extends Message> Write<T> writeProtos(Class<T> messageClass) {
   public static <T extends Message> Write<T> writeProtos(
       Class<T> messageClass,
       SerializableFunction<ValueInSingleWindow<T>, Map<String, String>> attributeFn) {
-    // TODO: Like in readProtos(), stop using ProtoCoder and instead format the payload directly.
+    // TODO: Like in readProtos(), stop using ProtoCoder and instead format the
+    // payload directly.
     return Write.newBuilder(formatPayloadUsingCoder(ProtoCoder.of(messageClass), attributeFn))
         .setDynamicDestinations(false)
         .build();
@@ -797,7 +821,8 @@ public static <T extends Message> Write<T> writeProtos(
    * Google Cloud Pub/Sub stream.
    */
   public static <T> Write<T> writeAvros(Class<T> clazz) {
-    // TODO: Like in readAvros(), stop using AvroCoder and instead format the payload directly.
+    // TODO: Like in readAvros(), stop using AvroCoder and instead format the
+    // payload directly.
     return Write.newBuilder(formatPayloadUsingCoder(AvroCoder.of(clazz)))
         .setDynamicDestinations(false)
         .build();
@@ -810,7 +835,8 @@ public static <T> Write<T> writeAvros(Class<T> clazz) {
   public static <T> Write<T> writeAvros(
       Class<T> clazz,
       SerializableFunction<ValueInSingleWindow<T>, Map<String, String>> attributeFn) {
-    // TODO: Like in readAvros(), stop using AvroCoder and instead format the payload directly.
+    // TODO: Like in readAvros(), stop using AvroCoder and instead format the
+    // payload directly.
     return Write.newBuilder(formatPayloadUsingCoder(AvroCoder.of(clazz), attributeFn))
         .setDynamicDestinations(false)
         .build();
@@ -1134,16 +1160,18 @@ public PCollection<T> expand(PBegin input) {
             "PubSubIO cannot be configured with both a dead letter topic and a bad record router");
       }
 
+      ValueProvider<PubsubTopic> topicProvider = getTopicProvider();
       @Nullable
       ValueProvider<TopicPath> topicPath =
-          getTopicProvider() == null
+          topicProvider == null
               ? null
-              : NestedValueProvider.of(getTopicProvider(), new TopicPathTranslator());
+              : NestedValueProvider.of(topicProvider, new TopicPathTranslator());
+      ValueProvider<PubsubSubscription> subscriptionProvider = getSubscriptionProvider();
       @Nullable
       ValueProvider<SubscriptionPath> subscriptionPath =
-          getSubscriptionProvider() == null
+          subscriptionProvider == null
               ? null
-              : NestedValueProvider.of(getSubscriptionProvider(), new SubscriptionPathTranslator());
+              : NestedValueProvider.of(subscriptionProvider, new SubscriptionPathTranslator());
       PubsubUnboundedSource source =
           new PubsubUnboundedSource(
               getClock(),
@@ -1177,7 +1205,7 @@ private PCollection<T> expandReadContinued(
           new SerializableFunction<PubsubMessage, T>() {
             // flag that reported metrics
             private final SerializableFunction<PubsubMessage, T> underlying =
-                Objects.requireNonNull(getParseFn());
+                checkStateNotNull(getParseFn());
             private transient boolean reportedMetrics = false;
 
             // public
@@ -1204,8 +1232,9 @@ public T apply(PubsubMessage input) {
               return underlying.apply(input);
             }
           };
+      ValueProvider<PubsubTopic> deadLetterTopicProvider = getDeadLetterTopicProvider();
       PCollection<T> read;
-      if (getDeadLetterTopicProvider() == null
+      if (deadLetterTopicProvider == null
           && (getBadRecordRouter() instanceof ThrowingBadRecordRouter)) {
         read = preParse.apply(MapElements.into(typeDescriptor).via(parseFnWrapped));
       } else {
@@ -1234,7 +1263,8 @@ public T apply(PubsubMessage input) {
           // Write out failures to the provided dead-letter topic.
           result
               .failures()
-              // Since the stack trace could easily exceed Pub/Sub limits, we need to remove it from
+              // Since the stack trace could easily exceed Pub/Sub limits, we need to remove
+              // it from
               // the attributes.
               .apply(
                   "PubsubIO.Read/Map/Remove-Stack-Trace-Attribute",
@@ -1254,7 +1284,9 @@ public T apply(PubsubMessage input) {
                             ImmutableMap<String, String> attributes =
                                 ImmutableMap.<String, String>builder()
                                     .put("exceptionClassName", throwable.getClass().getName())
-                                    .put("exceptionMessage", throwable.getMessage())
+                                    .put(
+                                        "exceptionMessage",
+                                        MoreObjects.firstNonNull(throwable.getMessage(), ""))
                                     .put("pubsubMessageId", messageId)
                                     .build();
 
@@ -1266,7 +1298,7 @@ public T apply(PubsubMessage input) {
                       .via(kv -> new PubsubMessage(kv.getKey().getPayload(), kv.getValue())))
               .apply(
                   writeMessages()
-                      .to(getDeadLetterTopicProvider().get().asPath())
+                      .to(checkStateNotNull(deadLetterTopicProvider).get().asPath())
                       .withClientFactory(getPubsubClientFactory()));
         }
       }
@@ -1274,16 +1306,20 @@ public T apply(PubsubMessage input) {
     }
 
     @Override
-    public void validate(PipelineOptions options) {
+    public void validate(@Nullable PipelineOptions options) {
       if (!getValidate()) {
         return;
       }
+      if (options == null) {
+        return;
+      }
 
       PubsubOptions psOptions = options.as(PubsubOptions.class);
 
       // Validate the existence of the topic.
-      if (getTopicProvider() != null) {
-        PubsubTopic topic = getTopicProvider().get();
+      ValueProvider<PubsubTopic> topicProvider = getTopicProvider();
+      if (topicProvider != null) {
+        PubsubTopic topic = topicProvider.get();
         boolean topicExists = true;
         try (PubsubClient pubsubClient =
             getPubsubClientFactory()
@@ -1405,10 +1441,10 @@ static Builder<PubsubMessage> newBuilder() {
 
     @AutoValue.Builder
     abstract static class Builder<T> {
-      abstract Builder<T> setTopicProvider(ValueProvider<PubsubTopic> topicProvider);
+      abstract Builder<T> setTopicProvider(@Nullable ValueProvider<PubsubTopic> topicProvider);
 
       abstract Builder<T> setTopicFunction(
-          SerializableFunction<ValueInSingleWindow<T>, PubsubTopic> topicFunction);
+          @Nullable SerializableFunction<ValueInSingleWindow<T>, PubsubTopic> topicFunction);
 
       abstract Builder<T> setDynamicDestinations(boolean dynamicDestinations);
 
@@ -1546,7 +1582,7 @@ public Write<T> withTimestampAttribute(String timestampAttribute) {
      * attribute with the specified name. The value of the attribute is an opaque string.
      *
      * <p>If the output from this sink is being read by another Beam pipeline, then {@link
-     * PubsubIO.Read#withIdAttribute(String)} can be used to ensure that* the other source reads
+     * PubsubIO.Read#withIdAttribute(String)} can be used to ensure that the other source reads
      * these unique identifiers from the appropriate attribute.
      */
     public Write<T> withIdAttribute(String idAttribute) {
@@ -1582,10 +1618,11 @@ public PDone expand(PCollection<T> input) {
                 + "dynamic topic destinations.");
       }
 
+      ValueProvider<PubsubTopic> topicProvider = getTopicProvider();
       SerializableFunction<ValueInSingleWindow<T>, PubsubIO.PubsubTopic> topicFunction =
           getTopicFunction();
-      if (topicFunction == null && getTopicProvider() != null) {
-        topicFunction = v -> getTopicProvider().get();
+      if (topicFunction == null && topicProvider != null) {
+        topicFunction = v -> topicProvider.get();
       }
       int maxMessageSize = PUBSUB_MESSAGE_MAX_TOTAL_SIZE;
       if (input.isBounded() == PCollection.IsBounded.BOUNDED) {
@@ -1633,8 +1670,8 @@ public PDone expand(PCollection<T> input) {
           return pubsubMessages.apply(
               new PubsubUnboundedSink(
                   getPubsubClientFactory(),
-                  getTopicProvider() != null
-                      ? NestedValueProvider.of(getTopicProvider(), new TopicPathTranslator())
+                  topicProvider != null
+                      ? NestedValueProvider.of(topicProvider, new TopicPathTranslator())
                       : null,
                   getTimestampAttribute(),
                   getIdAttribute(),
@@ -1650,16 +1687,20 @@ public PDone expand(PCollection<T> input) {
     }
 
     @Override
-    public void validate(PipelineOptions options) {
+    public void validate(@Nullable PipelineOptions options) {
       if (!getValidate()) {
         return;
       }
+      if (options == null) {
+        return;
+      }
 
       PubsubOptions psOptions = options.as(PubsubOptions.class);
 
       // Validate the existence of the topic.
-      if (getTopicProvider() != null) {
-        PubsubTopic topic = getTopicProvider().get();
+      ValueProvider<PubsubTopic> topicProvider = getTopicProvider();
+      if (topicProvider != null) {
+        PubsubTopic topic = topicProvider.get();
         boolean topicExists = true;
         try (PubsubClient pubsubClient =
             getPubsubClientFactory()
@@ -1702,10 +1743,11 @@ private class OutgoingData {
       }
 
       // NOTE: A single publish request may only write to one ordering key.
-      // See https://cloud.google.com/pubsub/docs/publisher#using-ordering-keys for details.
-      private transient Map<KV<PubsubTopic, String>, OutgoingData> output;
+      // See https://cloud.google.com/pubsub/docs/publisher#using-ordering-keys for
+      // details.
+      private transient @Nullable Map<KV<PubsubTopic, String>, OutgoingData> output;
 
-      private transient PubsubClient pubsubClient;
+      private transient @Nullable PubsubClient pubsubClient;
 
       private int maxPublishBatchByteSize;
       private int maxPublishBatchSize;
@@ -1750,16 +1792,19 @@ public void processElement(@Element PubsubMessage message, @Timestamp Instant ti
         final int messageSize = msg.getMessage().getData().size();
 
         final PubsubTopic pubsubTopic;
-        if (getTopicProvider() != null) {
-          pubsubTopic = getTopicProvider().get();
+        ValueProvider<PubsubTopic> topicProvider = getTopicProvider();
+        if (topicProvider != null) {
+          pubsubTopic = topicProvider.get();
         } else {
-          pubsubTopic = PubsubTopic.fromPath(Preconditions.checkArgumentNotNull(msg.topic()));
+          pubsubTopic = PubsubTopic.fromPath(checkArgumentNotNull(msg.topic()));
         }
 
-        // Checking before adding the message stops us from violating max batch size or bytes
+        // Checking before adding the message stops us from violating max batch size or
+        // bytes
         String orderingKey = getPublishWithOrderingKey() ? msg.getMessage().getOrderingKey() : "";
         final OutgoingData currentTopicAndOrderingKeyOutput =
-            output.computeIfAbsent(KV.of(pubsubTopic, orderingKey), t -> new OutgoingData());
+            checkStateNotNull(output)
+                .computeIfAbsent(KV.of(pubsubTopic, orderingKey), t -> new OutgoingData());
         // TODO(sjvanrossum): https://github.com/apache/beam/issues/31800
         if (currentTopicAndOrderingKeyOutput.messages.size() >= maxPublishBatchSize
             || (!currentTopicAndOrderingKeyOutput.messages.isEmpty()
@@ -1776,18 +1821,24 @@ public void processElement(@Element PubsubMessage message, @Timestamp Instant ti
 
       @FinishBundle
       public void finishBundle() throws IOException {
-        for (Map.Entry<KV<PubsubTopic, String>, OutgoingData> entry : output.entrySet()) {
-          publish(entry.getKey().getKey(), entry.getValue().messages);
+        final Map<KV<PubsubTopic, String>, OutgoingData> output = this.output;
+        if (output != null) {
+          for (Map.Entry<KV<PubsubTopic, String>, OutgoingData> entry : output.entrySet()) {
+            publish(entry.getKey().getKey(), entry.getValue().messages);
+          }
+        }
+        this.output = null;
+        final PubsubClient pubsubClient = this.pubsubClient;
+        if (pubsubClient != null) {
+          pubsubClient.close();
         }
-        output = null;
-        pubsubClient.close();
-        pubsubClient = null;
+        this.pubsubClient = null;
       }
 
       private void publish(PubsubTopic topic, List<OutgoingMessage> messages) throws IOException {
         int n =
-            pubsubClient.publish(
-                PubsubClient.topicPathFromName(topic.project, topic.topic), messages);
+            checkStateNotNull(pubsubClient)
+                .publish(PubsubClient.topicPathFromName(topic.project, topic.topic), messages);
         checkState(n == messages.size());
       }
 
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubJsonClient.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubJsonClient.java
index f36e94360996..d0f9635391f9 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubJsonClient.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubJsonClient.java
@@ -17,7 +17,7 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
-import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 
 import com.google.api.client.googleapis.json.GoogleJsonResponseException;
 import com.google.api.client.http.HttpRequestInitializer;
@@ -51,14 +51,10 @@
 import org.apache.beam.sdk.schemas.Schema;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.annotations.VisibleForTesting;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.MoreObjects;
-import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Strings;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
 import org.checkerframework.checker.nullness.qual.Nullable;
 
 /** A Pubsub client using JSON transport. */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubJsonClient extends PubsubClient {
 
   private static class PubsubJsonClientFactory implements PubsubClientFactory {
@@ -85,7 +81,7 @@ public PubsubClient newClient(
         @Nullable String timestampAttribute,
         @Nullable String idAttribute,
         PubsubOptions options,
-        String rootUrlOverride)
+        @Nullable String rootUrlOverride)
         throws IOException {
       Pubsub pubsub =
           new Pubsub.Builder(
@@ -163,8 +159,9 @@ private Map<String, String> getMessageAttributes(OutgoingMessage outgoingMessage
       attributes.put(
           timestampAttribute, String.valueOf(outgoingMessage.getTimestampMsSinceEpoch()));
     }
-    if (idAttribute != null && !Strings.isNullOrEmpty(outgoingMessage.recordId())) {
-      attributes.put(idAttribute, outgoingMessage.recordId());
+    String recordId = outgoingMessage.recordId();
+    if (idAttribute != null && recordId != null && !recordId.isEmpty()) {
+      attributes.put(idAttribute, recordId);
     }
     return attributes;
   }
@@ -181,45 +178,51 @@ public List<IncomingMessage> pull(
         new PullRequest().setReturnImmediately(returnImmediately).setMaxMessages(batchSize);
     PullResponse response =
         pubsub.projects().subscriptions().pull(subscription.getPath(), request).execute();
-    if (response.getReceivedMessages() == null || response.getReceivedMessages().isEmpty()) {
+    List<ReceivedMessage> receivedMessages = response.getReceivedMessages();
+    if (receivedMessages == null || receivedMessages.isEmpty()) {
       return ImmutableList.of();
     }
-    List<IncomingMessage> incomingMessages = new ArrayList<>(response.getReceivedMessages().size());
-    for (ReceivedMessage message : response.getReceivedMessages()) {
+    List<IncomingMessage> incomingMessages = new ArrayList<>(receivedMessages.size());
+    for (ReceivedMessage message : receivedMessages) {
       PubsubMessage pubsubMessage = message.getMessage();
-      Map<String, String> attributes;
-      if (pubsubMessage.getAttributes() != null) {
-        attributes = pubsubMessage.getAttributes();
-      } else {
+      if (pubsubMessage == null) {
+        continue;
+      }
+      Map<String, String> attributes = pubsubMessage.getAttributes();
+      if (attributes == null) {
         attributes = new HashMap<>();
       }
 
       // Payload.
-      byte[] elementBytes = pubsubMessage.getData() == null ? null : pubsubMessage.decodeData();
-      if (elementBytes == null) {
-        elementBytes = new byte[0];
-      }
+      String dataStr = pubsubMessage.getData();
+      byte[] elementBytes = (dataStr == null) ? new byte[0] : pubsubMessage.decodeData();
 
       // Timestamp.
       long timestampMsSinceEpoch;
-      if (Strings.isNullOrEmpty(timestampAttribute)) {
-        timestampMsSinceEpoch = parseTimestampAsMsSinceEpoch(message.getMessage().getPublishTime());
+      if (timestampAttribute == null || timestampAttribute.isEmpty()) {
+        String publishTime = pubsubMessage.getPublishTime();
+        if (publishTime == null) {
+          throw new IllegalStateException("Received message missing publishTime");
+        }
+        timestampMsSinceEpoch = parseTimestampAsMsSinceEpoch(publishTime);
       } else {
         timestampMsSinceEpoch = extractTimestampAttribute(timestampAttribute, attributes);
       }
 
       // Ack id.
       String ackId = message.getAckId();
-      checkState(!Strings.isNullOrEmpty(ackId));
+      if (ackId == null || ackId.isEmpty()) {
+        throw new IllegalStateException("Received message missing ackId");
+      }
 
       // Record id, if any.
       @Nullable String recordId = null;
       if (idAttribute != null) {
         recordId = attributes.get(idAttribute);
       }
-      if (Strings.isNullOrEmpty(recordId)) {
+      if (recordId == null || recordId.isEmpty()) {
         // Fall back to the Pubsub provided message id.
-        recordId = pubsubMessage.getMessageId();
+        recordId = checkStateNotNull(pubsubMessage.getMessageId(), "Message ID is missing");
       }
 
       com.google.pubsub.v1.PubsubMessage.Builder protoMessage =
@@ -229,8 +232,9 @@ public List<IncomingMessage> pull(
       // {@link PubsubMessage} uses `null` or empty string to represent no ordering key.
       // {@link com.google.pubsub.v1.PubsubMessage} does not track string field presence and uses
       // empty string as a default.
-      if (pubsubMessage.getOrderingKey() != null) {
-        protoMessage.setOrderingKey(pubsubMessage.getOrderingKey());
+      String orderingKey = pubsubMessage.getOrderingKey();
+      if (orderingKey != null) {
+        protoMessage.setOrderingKey(orderingKey);
       }
       incomingMessages.add(
           IncomingMessage.of(
@@ -289,19 +293,25 @@ public void deleteTopic(TopicPath topic) throws IOException {
   public List<TopicPath> listTopics(ProjectPath project) throws IOException {
     Topics.List request = pubsub.projects().topics().list(project.getPath());
     ListTopicsResponse response = request.execute();
-    if (response.getTopics() == null || response.getTopics().isEmpty()) {
+    List<Topic> topicsList = response.getTopics();
+    if (topicsList == null || topicsList.isEmpty()) {
       return ImmutableList.of();
     }
-    List<TopicPath> topics = new ArrayList<>(response.getTopics().size());
+    List<TopicPath> topics = new ArrayList<>(topicsList.size());
     while (true) {
-      for (Topic topic : response.getTopics()) {
+      for (Topic topic : topicsList) {
         topics.add(topicPathFromPath(topic.getName()));
       }
-      if (Strings.isNullOrEmpty(response.getNextPageToken())) {
+      String nextPageToken = response.getNextPageToken();
+      if (nextPageToken == null || nextPageToken.isEmpty()) {
         break;
       }
-      request.setPageToken(response.getNextPageToken());
+      request.setPageToken(nextPageToken);
       response = request.execute();
+      topicsList = response.getTopics();
+      if (topicsList == null) {
+        break;
+      }
     }
     return topics;
   }
@@ -345,21 +355,28 @@ public List<SubscriptionPath> listSubscriptions(ProjectPath project, TopicPath t
       throws IOException {
     Subscriptions.List request = pubsub.projects().subscriptions().list(project.getPath());
     ListSubscriptionsResponse response = request.execute();
-    if (response.getSubscriptions() == null || response.getSubscriptions().isEmpty()) {
+    List<Subscription> subscriptionsList = response.getSubscriptions();
+    if (subscriptionsList == null || subscriptionsList.isEmpty()) {
       return ImmutableList.of();
     }
-    List<SubscriptionPath> subscriptions = new ArrayList<>(response.getSubscriptions().size());
+    List<SubscriptionPath> subscriptions = new ArrayList<>(subscriptionsList.size());
     while (true) {
-      for (Subscription subscription : response.getSubscriptions()) {
-        if (subscription.getTopic().equals(topic.getPath())) {
+      for (Subscription subscription : subscriptionsList) {
+        String subTopic = subscription.getTopic();
+        if (subTopic != null && subTopic.equals(topic.getPath())) {
           subscriptions.add(subscriptionPathFromPath(subscription.getName()));
         }
       }
-      if (Strings.isNullOrEmpty(response.getNextPageToken())) {
+      String nextPageToken = response.getNextPageToken();
+      if (nextPageToken == null || nextPageToken.isEmpty()) {
         break;
       }
-      request.setPageToken(response.getNextPageToken());
+      request.setPageToken(nextPageToken);
       response = request.execute();
+      subscriptionsList = response.getSubscriptions();
+      if (subscriptionsList == null) {
+        break;
+      }
     }
     return subscriptions;
   }
@@ -391,13 +408,14 @@ public void deleteSchema(SchemaPath schemaPath) throws IOException {
 
   /** Return {@link SchemaPath} from {@link TopicPath} if exists. */
   @Override
-  public SchemaPath getSchemaPath(TopicPath topicPath) throws IOException {
+  public @Nullable SchemaPath getSchemaPath(TopicPath topicPath) throws IOException {
     Topic topic = pubsub.projects().topics().get(topicPath.getPath()).execute();
-    if (topic.getSchemaSettings() == null) {
+    com.google.api.services.pubsub.model.SchemaSettings schemaSettings = topic.getSchemaSettings();
+    if (schemaSettings == null) {
       return null;
     }
-    String schemaPath = topic.getSchemaSettings().getSchema();
-    if (schemaPath.equals(SchemaPath.DELETED_SCHEMA_PATH)) {
+    String schemaPath = schemaSettings.getSchema();
+    if (schemaPath == null || schemaPath.equals(SchemaPath.DELETED_SCHEMA_PATH)) {
       return null;
     }
     return PubsubClient.schemaPathFromPath(schemaPath);
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessage.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessage.java
index 779a9b847874..7732839181e6 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessage.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessage.java
@@ -17,31 +17,32 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
-import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
-
 import com.google.auto.value.AutoValue;
 import java.util.Map;
 import org.checkerframework.checker.nullness.qual.Nullable;
+import org.checkerframework.dataflow.qual.Pure;
 
 /**
  * Class representing a Pub/Sub message. Each message contains a single message payload, a map of
  * attached attributes, a message id and an ordering key.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubMessage {
   @AutoValue
   abstract static class Impl {
+    @Pure
     abstract @Nullable String getTopic();
 
+    @Pure
     @SuppressWarnings("mutable")
     abstract byte[] getPayload();
 
+    @Pure
     abstract @Nullable Map<String, String> getAttributeMap();
 
+    @Pure
     abstract @Nullable String getMessageId();
 
+    @Pure
     abstract @Nullable String getOrderingKey();
 
     static Impl create(
@@ -87,27 +88,32 @@ public PubsubMessage withTopic(String topic) {
             impl.getOrderingKey()));
   }
 
+  @Pure
   public @Nullable String getTopic() {
     return impl.getTopic();
   }
 
   /** Returns the main PubSub message. */
+  @Pure
   public byte[] getPayload() {
     return impl.getPayload();
   }
 
   /** Returns the given attribute value. If not such attribute exists, returns null. */
+  @Pure
   public @Nullable String getAttribute(String attribute) {
-    checkNotNull(attribute, "attribute");
-    return impl.getAttributeMap().get(attribute);
+    Map<String, String> attributeMap = impl.getAttributeMap();
+    return attributeMap == null ? null : attributeMap.get(attribute);
   }
 
   /** Returns the full map of attributes. This is an unmodifiable map. */
+  @Pure
   public @Nullable Map<String, String> getAttributeMap() {
     return impl.getAttributeMap();
   }
 
   /** Returns the messageId of the message populated by Cloud Pub/Sub. */
+  @Pure
   public @Nullable String getMessageId() {
     return impl.getMessageId();
   }
@@ -123,6 +129,7 @@ public PubsubMessage withOrderingKey(@Nullable String orderingKey) {
   }
 
   /** Returns the ordering key of the message. */
+  @Pure
   public @Nullable String getOrderingKey() {
     return impl.getOrderingKey();
   }
@@ -133,7 +140,7 @@ public String toString() {
   }
 
   @Override
-  public boolean equals(Object other) {
+  public boolean equals(@Nullable Object other) {
     if (!(other instanceof PubsubMessage)) {
       return false;
     }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageToRow.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageToRow.java
index d860bfba95ec..c005253110c7 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageToRow.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageToRow.java
@@ -19,6 +19,8 @@
 
 import static java.util.stream.Collectors.toList;
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubSchemaIOProvider.ATTRIBUTE_ARRAY_ENTRY_SCHEMA;
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
 
 import com.google.auto.value.AutoValue;
@@ -26,7 +28,6 @@
 import java.util.List;
 import java.util.Map;
 import java.util.stream.Collectors;
-import javax.annotation.Nullable;
 import org.apache.beam.sdk.annotations.Internal;
 import org.apache.beam.sdk.schemas.Schema;
 import org.apache.beam.sdk.schemas.Schema.TypeName;
@@ -41,14 +42,12 @@
 import org.apache.beam.sdk.values.TupleTag;
 import org.apache.beam.sdk.values.TupleTagList;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableList;
+import org.checkerframework.checker.nullness.qual.Nullable;
 import org.joda.time.Instant;
 
 /** Read side converter for {@link PubsubMessage} with JSON/AVRO payload. */
 @Internal
 @AutoValue
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 abstract class PubsubMessageToRow extends PTransform<PCollection<PubsubMessage>, PCollectionTuple>
     implements Serializable {
   interface SerializerProvider extends SerializableFunction<Schema, PayloadSerializer> {}
@@ -94,7 +93,10 @@ public PCollectionTuple expand(PCollection<PubsubMessage> input) {
             ParDo.of(
                     useFlatSchema()
                         ? new FlatSchemaPubsubMessageToRow(
-                            messageSchema(), useDlq(), serializerProvider())
+                            messageSchema(),
+                            useDlq(),
+                            checkArgumentNotNull(
+                                serializerProvider(), "Flat schema requires serializerProvider"))
                         : new NestedSchemaPubsubMessageToRow(
                             messageSchema(), useDlq(), serializerProvider()))
                 .withOutputTags(
@@ -133,7 +135,8 @@ protected FlatSchemaPubsubMessageToRow(
      * Get the value for a field from a given payload in the order they're specified in the flat
      * schema.
      */
-    private Object getValueForFieldFlatSchema(Schema.Field field, Instant timestamp, Row payload) {
+    private @Nullable Object getValueForFieldFlatSchema(
+        Schema.Field field, Instant timestamp, Row payload) {
       String fieldName = field.getName();
       if (TIMESTAMP_FIELD.equals(fieldName)) {
         return timestamp;
@@ -147,9 +150,10 @@ public void processElement(
         @Element PubsubMessage element, @Timestamp Instant timestamp, MultiOutputReceiver o) {
       try {
         Row payload = payloadSerializer.deserialize(element.getPayload());
-        List<Object> values =
+        List<@Nullable Object> values =
             messageSchema.getFields().stream()
-                .map(field -> getValueForFieldFlatSchema(field, timestamp, payload))
+                .<@Nullable Object>map(
+                    field -> getValueForFieldFlatSchema(field, timestamp, payload))
                 .collect(toList());
         o.get(MAIN_TAG).output(Row.withSchema(messageSchema).addValues(values).build());
       } catch (Exception e) {
@@ -186,7 +190,8 @@ private NestedSchemaPubsubMessageToRow(
       } else {
         checkArgument(
             messageSchema.getField(PAYLOAD_FIELD).getType().getTypeName().equals(TypeName.ROW));
-        Schema payloadSchema = messageSchema.getField(PAYLOAD_FIELD).getType().getRowSchema();
+        Schema payloadSchema =
+            checkStateNotNull(messageSchema.getField(PAYLOAD_FIELD).getType().getRowSchema());
         this.payloadSerializer = serializerProvider.apply(payloadSchema);
       }
     }
@@ -198,7 +203,13 @@ private Object maybeDeserialize(byte[] payload) {
       return payloadSerializer.deserialize(payload);
     }
 
-    private Object handleAttributes(Map<String, String> attributeMap) {
+    private @Nullable Object handleAttributes(@Nullable Map<String, String> attributeMap) {
+      if (attributeMap == null) {
+        if (messageSchema.getField(ATTRIBUTES_FIELD).getType().getTypeName().isMapType()) {
+          return null;
+        }
+        return ImmutableList.of();
+      }
       if (messageSchema.getField(ATTRIBUTES_FIELD).getType().getTypeName().isMapType()) {
         return attributeMap;
       }
@@ -209,8 +220,11 @@ private Object handleAttributes(Map<String, String> attributeMap) {
     }
 
     /** Get the value for a field int the order they're specified in the nested schema. */
-    private Object getValueForFieldNestedSchema(
-        Schema.Field field, Instant timestamp, Map<String, String> attributeMap, byte[] payload) {
+    private @Nullable Object getValueForFieldNestedSchema(
+        Schema.Field field,
+        Instant timestamp,
+        @Nullable Map<String, String> attributeMap,
+        byte[] payload) {
       switch (field.getName()) {
         case TIMESTAMP_FIELD:
           return timestamp;
@@ -232,9 +246,9 @@ private Object getValueForFieldNestedSchema(
     public void processElement(
         @Element PubsubMessage element, @Timestamp Instant timestamp, MultiOutputReceiver o) {
       try {
-        List<Object> values =
+        List<@Nullable Object> values =
             messageSchema.getFields().stream()
-                .map(
+                .<@Nullable Object>map(
                     field ->
                         getValueForFieldNestedSchema(
                             field, timestamp, element.getAttributeMap(), element.getPayload()))
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdAndOrderingKeyCoder.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdAndOrderingKeyCoder.java
index 968d76584bc3..d2ba0b9446f2 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdAndOrderingKeyCoder.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdAndOrderingKeyCoder.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+
 import com.google.protobuf.Timestamp;
 import java.io.IOException;
 import java.io.InputStream;
@@ -30,6 +32,7 @@
 import org.apache.beam.sdk.coders.StringUtf8Coder;
 import org.apache.beam.sdk.extensions.protobuf.ProtoCoder;
 import org.apache.beam.sdk.values.TypeDescriptor;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A coder for PubsubMessage including all fields of a PubSub message from server.
@@ -37,22 +40,20 @@
  * <p>Maintainers should prefer {@link PubsubMessageSchemaCoder} over this coder when adding
  * features to {@link PubsubIO}.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubMessageWithAttributesAndMessageIdAndOrderingKeyCoder
     extends CustomCoder<PubsubMessage> {
   // A message's payload cannot be null
   private static final Coder<byte[]> PAYLOAD_CODER = ByteArrayCoder.of();
   // A message's attributes can be null.
-  private static final Coder<Map<String, String>> ATTRIBUTES_CODER =
+  private static final Coder<@Nullable Map<String, String>> ATTRIBUTES_CODER =
       NullableCoder.of(MapCoder.of(StringUtf8Coder.of(), StringUtf8Coder.of()));
   // A message's messageId cannot be null
   private static final Coder<String> MESSAGE_ID_CODER = StringUtf8Coder.of();
   // A message's publish time, populated by server
   private static final Coder<Timestamp> PUBLISH_TIME_CODER = ProtoCoder.of(Timestamp.class);
   // A message's ordering key can be null
-  private static final Coder<String> ORDERING_KEY_CODER = NullableCoder.of(StringUtf8Coder.of());
+  private static final Coder<@Nullable String> ORDERING_KEY_CODER =
+      NullableCoder.of(StringUtf8Coder.of());
 
   public static Coder<PubsubMessage> of(TypeDescriptor<PubsubMessage> ignored) {
     return of();
@@ -66,7 +67,9 @@ public static PubsubMessageWithAttributesAndMessageIdAndOrderingKeyCoder of() {
   public void encode(PubsubMessage value, OutputStream outStream) throws IOException {
     PAYLOAD_CODER.encode(value.getPayload(), outStream);
     ATTRIBUTES_CODER.encode(value.getAttributeMap(), outStream);
-    MESSAGE_ID_CODER.encode(value.getMessageId(), outStream);
+    MESSAGE_ID_CODER.encode(
+        checkArgumentNotNull(value.getMessageId(), "Cannot encode PubsubMessage without messageId"),
+        outStream);
     // TODO(discuss what to do with publish_time field)
     PUBLISH_TIME_CODER.encode(Timestamp.getDefaultInstance(), outStream);
     ORDERING_KEY_CODER.encode(value.getOrderingKey(), outStream);
@@ -75,10 +78,10 @@ public void encode(PubsubMessage value, OutputStream outStream) throws IOExcepti
   @Override
   public PubsubMessage decode(InputStream inStream) throws IOException {
     byte[] payload = PAYLOAD_CODER.decode(inStream);
-    Map<String, String> attributes = ATTRIBUTES_CODER.decode(inStream);
+    @Nullable Map<String, String> attributes = ATTRIBUTES_CODER.decode(inStream);
     String messageId = MESSAGE_ID_CODER.decode(inStream);
     PUBLISH_TIME_CODER.decode(inStream);
-    String orderingKey = ORDERING_KEY_CODER.decode(inStream);
+    @Nullable String orderingKey = ORDERING_KEY_CODER.decode(inStream);
     return new PubsubMessage(payload, attributes, messageId, orderingKey);
   }
 }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdCoder.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdCoder.java
index 803ff83583ce..32449d0425e8 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdCoder.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesAndMessageIdCoder.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -28,6 +30,7 @@
 import org.apache.beam.sdk.coders.NullableCoder;
 import org.apache.beam.sdk.coders.StringUtf8Coder;
 import org.apache.beam.sdk.values.TypeDescriptor;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A coder for PubsubMessage including attributes and the message id from the PubSub server.
@@ -35,14 +38,11 @@
  * <p>Maintainers should prefer {@link PubsubMessageSchemaCoder} over this coder when adding
  * features to {@link PubsubIO}.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubMessageWithAttributesAndMessageIdCoder extends CustomCoder<PubsubMessage> {
   // A message's payload cannot be null
   private static final Coder<byte[]> PAYLOAD_CODER = ByteArrayCoder.of();
   // A message's attributes can be null.
-  private static final Coder<Map<String, String>> ATTRIBUTES_CODER =
+  private static final Coder<@Nullable Map<String, String>> ATTRIBUTES_CODER =
       NullableCoder.of(MapCoder.of(StringUtf8Coder.of(), StringUtf8Coder.of()));
   // A message's messageId cannot be null
   private static final Coder<String> MESSAGE_ID_CODER = StringUtf8Coder.of();
@@ -59,13 +59,15 @@ public static PubsubMessageWithAttributesAndMessageIdCoder of() {
   public void encode(PubsubMessage value, OutputStream outStream) throws IOException {
     PAYLOAD_CODER.encode(value.getPayload(), outStream);
     ATTRIBUTES_CODER.encode(value.getAttributeMap(), outStream);
-    MESSAGE_ID_CODER.encode(value.getMessageId(), outStream);
+    MESSAGE_ID_CODER.encode(
+        checkArgumentNotNull(value.getMessageId(), "Cannot encode PubsubMessage without messageId"),
+        outStream);
   }
 
   @Override
   public PubsubMessage decode(InputStream inStream) throws IOException {
     byte[] payload = PAYLOAD_CODER.decode(inStream);
-    Map<String, String> attributes = ATTRIBUTES_CODER.decode(inStream);
+    @Nullable Map<String, String> attributes = ATTRIBUTES_CODER.decode(inStream);
     String messageId = MESSAGE_ID_CODER.decode(inStream);
     return new PubsubMessage(payload, attributes, messageId);
   }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesCoder.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesCoder.java
index 9dd3ab56a72a..38b7661fba9b 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesCoder.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithAttributesCoder.java
@@ -28,6 +28,7 @@
 import org.apache.beam.sdk.coders.NullableCoder;
 import org.apache.beam.sdk.coders.StringUtf8Coder;
 import org.apache.beam.sdk.values.TypeDescriptor;
+import org.checkerframework.checker.nullness.qual.Nullable;
 
 /**
  * A coder for PubsubMessage including attributes.
@@ -35,14 +36,11 @@
  * <p>Maintainers should prefer {@link PubsubMessageSchemaCoder} over this coder when adding
  * features to {@link PubsubIO}.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubMessageWithAttributesCoder extends CustomCoder<PubsubMessage> {
   // A message's payload can not be null
   private static final Coder<byte[]> PAYLOAD_CODER = ByteArrayCoder.of();
   // A message's attributes can be null.
-  private static final Coder<Map<String, String>> ATTRIBUTES_CODER =
+  private static final Coder<@Nullable Map<String, String>> ATTRIBUTES_CODER =
       NullableCoder.of(MapCoder.of(StringUtf8Coder.of(), StringUtf8Coder.of()));
 
   public static Coder<PubsubMessage> of(TypeDescriptor<PubsubMessage> ignored) {
@@ -58,6 +56,7 @@ public void encode(PubsubMessage value, OutputStream outStream) throws IOExcepti
     encode(value, outStream, Context.NESTED);
   }
 
+  @Override
   public void encode(PubsubMessage value, OutputStream outStream, Context context)
       throws IOException {
     PAYLOAD_CODER.encode(value.getPayload(), outStream);
@@ -72,7 +71,7 @@ public PubsubMessage decode(InputStream inStream) throws IOException {
   @Override
   public PubsubMessage decode(InputStream inStream, Context context) throws IOException {
     byte[] payload = PAYLOAD_CODER.decode(inStream);
-    Map<String, String> attributes = ATTRIBUTES_CODER.decode(inStream, context);
+    @Nullable Map<String, String> attributes = ATTRIBUTES_CODER.decode(inStream, context);
     return new PubsubMessage(payload, attributes);
   }
 }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithMessageIdCoder.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithMessageIdCoder.java
index 7016146b3671..d150d8ac76cb 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithMessageIdCoder.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubMessageWithMessageIdCoder.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.OutputStream;
@@ -33,9 +35,6 @@
  * <p>Maintainers should prefer {@link PubsubMessageSchemaCoder} over this coder when adding
  * features to {@link PubsubIO}.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubMessageWithMessageIdCoder extends CustomCoder<PubsubMessage> {
   private static final Coder<byte[]> PAYLOAD_CODER = ByteArrayCoder.of();
   // A message's messageId cannot be null
@@ -48,7 +47,9 @@ public static PubsubMessageWithMessageIdCoder of() {
   @Override
   public void encode(PubsubMessage value, OutputStream outStream) throws IOException {
     PAYLOAD_CODER.encode(value.getPayload(), outStream);
-    MESSAGE_ID_CODER.encode(value.getMessageId(), outStream);
+    MESSAGE_ID_CODER.encode(
+        checkArgumentNotNull(value.getMessageId(), "Cannot encode PubsubMessage without messageId"),
+        outStream);
   }
 
   @Override
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubReadSchemaTransformProvider.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubReadSchemaTransformProvider.java
index c690115045bd..3efe18a08f32 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubReadSchemaTransformProvider.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubReadSchemaTransformProvider.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+
 import com.google.api.client.util.Clock;
 import com.google.auto.service.AutoService;
 import java.io.Serializable;
@@ -247,17 +249,23 @@ void setClock(@Nullable Clock clock) {
       this.clock = clock;
     }
 
-    @SuppressWarnings("nullness")
     PubsubIO.Read<PubsubMessage> buildPubsubRead() {
       PubsubIO.Read<PubsubMessage> pubsubRead =
           (configuration.getAttributes() == null && configuration.getAttributesMap() == null)
               ? PubsubIO.readMessages()
               : PubsubIO.readMessagesWithAttributes();
-      if (!Strings.isNullOrEmpty(configuration.getTopic())) {
-        pubsubRead = pubsubRead.fromTopic(configuration.getTopic());
+      String topic = configuration.getTopic();
+      if (topic != null && !topic.isEmpty()) {
+        pubsubRead = pubsubRead.fromTopic(topic);
       } else {
-        pubsubRead = pubsubRead.fromSubscription(configuration.getSubscription());
+        String subscription = configuration.getSubscription();
+        pubsubRead =
+            pubsubRead.fromSubscription(
+                checkArgumentNotNull(
+                    subscription, "Either topic or subscription must be specified"));
       }
+      final PubsubTestClientFactory clientFactory = this.clientFactory;
+      final Clock clock = this.clock;
       if (clientFactory != null && clock != null) {
         pubsubRead = pubsubRead.withClientFactory(clientFactory);
         pubsubRead = clientFactory.setClock(pubsubRead, clock);
@@ -265,11 +273,13 @@ PubsubIO.Read<PubsubMessage> buildPubsubRead() {
         throw new IllegalArgumentException(
             "Both PubsubTestClientFactory and Clock need to be specified for testing, but only one is provided");
       }
-      if (!Strings.isNullOrEmpty(configuration.getIdAttribute())) {
-        pubsubRead = pubsubRead.withIdAttribute(configuration.getIdAttribute());
+      String idAttribute = configuration.getIdAttribute();
+      if (idAttribute != null && !idAttribute.isEmpty()) {
+        pubsubRead = pubsubRead.withIdAttribute(idAttribute);
       }
-      if (!Strings.isNullOrEmpty(configuration.getTimestampAttribute())) {
-        pubsubRead = pubsubRead.withTimestampAttribute(configuration.getTimestampAttribute());
+      String timestampAttribute = configuration.getTimestampAttribute();
+      if (timestampAttribute != null && !timestampAttribute.isEmpty()) {
+        pubsubRead = pubsubRead.withTimestampAttribute(timestampAttribute);
       }
       return pubsubRead;
     }
@@ -277,11 +287,9 @@ PubsubIO.Read<PubsubMessage> buildPubsubRead() {
     @Override
     public PCollectionRowTuple expand(PCollectionRowTuple input) {
       PubsubIO.Read<PubsubMessage> pubsubRead = buildPubsubRead();
-      @SuppressWarnings("nullness")
-      String errorOutput =
-          configuration.getErrorHandling() == null
-              ? null
-              : configuration.getErrorHandling().getOutput();
+      PubsubReadSchemaTransformConfiguration.ErrorHandling errorHandling =
+          configuration.getErrorHandling();
+      String errorOutput = errorHandling == null ? null : errorHandling.getOutput();
 
       PCollectionTuple outputTuple =
           input
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubRowToMessage.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubRowToMessage.java
index da3ee89de0d8..0085662fd3b6 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubRowToMessage.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubRowToMessage.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
 
 import com.google.auto.value.AutoValue;
@@ -24,10 +26,8 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Objects;
 import java.util.Optional;
 import java.util.stream.Collectors;
-import javax.annotation.Nullable;
 import org.apache.beam.sdk.annotations.Internal;
 import org.apache.beam.sdk.schemas.Schema;
 import org.apache.beam.sdk.schemas.Schema.Field;
@@ -43,6 +43,7 @@
 import org.apache.beam.sdk.values.TupleTag;
 import org.apache.beam.sdk.values.TupleTagList;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Throwables;
+import org.checkerframework.checker.nullness.qual.Nullable;
 import org.joda.time.DateTime;
 import org.joda.time.Instant;
 import org.joda.time.ReadableDateTime;
@@ -51,9 +52,6 @@
 /** Write side {@link Row} to {@link PubsubMessage} converter. */
 @Internal
 @AutoValue
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 abstract class PubsubRowToMessage extends PTransform<PCollection<Row>, PCollectionTuple> {
 
   static Builder builder() {
@@ -88,18 +86,15 @@ static Builder builder() {
    * The {@link PayloadSerializer} to {@link PayloadSerializer#serialize(Row)} the payload or user
    * fields row.
    */
-  @Nullable
-  abstract PayloadSerializer getPayloadSerializer();
+  abstract @Nullable PayloadSerializer getPayloadSerializer();
 
   /** The name of the attribute to apply to the {@link PubsubMessage}. */
-  @Nullable
-  abstract String getTargetTimestampAttributeName();
+  abstract @Nullable String getTargetTimestampAttributeName();
 
   /**
    * Use for testing, simplify assertions of generated timestamp when input lacks a timestamp field.
    */
-  @Nullable
-  abstract Instant getMockInstant();
+  abstract @Nullable Instant getMockInstant();
 
   /** Generates {@link Schema} of the {@link #ERROR} {@link PCollection}. */
   static Schema errorSchema(Schema inputSchema) {
@@ -345,9 +340,9 @@ static FieldMatcher of(String name, FieldType fieldType) {
 
     private final String name;
 
-    @Nullable private final TypeName typeName;
+    private final @Nullable TypeName typeName;
 
-    @Nullable private final FieldType fieldType;
+    private final @Nullable FieldType fieldType;
 
     private FieldMatcher(String name, @Nullable TypeName typeName, @Nullable FieldType fieldType) {
       this.name = name;
@@ -379,7 +374,10 @@ boolean match(Schema schema) {
       if (typeName != null) {
         return field.getType().getTypeName().equals(typeName);
       }
-      return fieldType.equals(field.getType());
+      if (fieldType != null) {
+        return fieldType.equals(field.getType());
+      }
+      return true;
     }
   }
 
@@ -404,10 +402,10 @@ static class PubsubRowToMessageDoFn extends DoFn<Row, PubsubMessage> {
     private final String payloadKeyName;
     private final Schema errorSchema;
 
-    @Nullable private final String targetTimestampKeyName;
-    @Nullable private final PayloadSerializer payloadSerializer;
+    private final @Nullable String targetTimestampKeyName;
+    private final @Nullable PayloadSerializer payloadSerializer;
 
-    @Nullable private final Instant mockInstant;
+    private final @Nullable Instant mockInstant;
 
     PubsubRowToMessageDoFn(
         String attributesKeyName,
@@ -449,7 +447,7 @@ public void process(@Element Row row, MultiOutputReceiver receiver) {
         Row error =
             Row.withSchema(errorSchema)
                 .withFieldValue(ERROR_DATA_FIELD_NAME, row)
-                .withFieldValue(ERROR_MESSAGE_FIELD.getName(), message)
+                .withFieldValue(ERROR_MESSAGE_FIELD.getName(), message != null ? message : "")
                 .withFieldValue(ERROR_STACK_TRACE_FIELD.getName(), stackTrace)
                 .build();
 
@@ -465,7 +463,8 @@ Map<String, String> attributesWithoutTimestamp(Row row) {
       if (!row.getSchema().hasField(attributesKeyName)) {
         return new HashMap<>();
       }
-      return row.getMap(attributesKeyName);
+      Map<String, String> map = row.getMap(attributesKeyName);
+      return map == null ? new HashMap<>() : map;
     }
 
     /**
@@ -482,7 +481,10 @@ String timestampAsString(Row row) {
      */
     ReadableDateTime timestamp(Row row) {
       if (row.getSchema().hasField(sourceTimestampKeyName)) {
-        return row.getDateTime(sourceTimestampKeyName);
+        ReadableDateTime dt = row.getDateTime(sourceTimestampKeyName);
+        if (dt != null) {
+          return dt;
+        }
       }
       Instant instant = Instant.now();
       if (mockInstant != null) {
@@ -503,9 +505,10 @@ ReadableDateTime timestamp(Row row) {
     byte[] payload(Row row) {
       if (SchemaReflection.of(row.getSchema())
           .matchesAll(FieldMatcher.of(payloadKeyName, PAYLOAD_BYTES_TYPE_NAME))) {
-        return row.getBytes(payloadKeyName);
+        return checkArgumentNotNull(
+            row.getBytes(payloadKeyName), "Payload field '%s' cannot be null", payloadKeyName);
       }
-      return Objects.requireNonNull(payloadSerializer).serialize(serializableRow(row));
+      return checkStateNotNull(payloadSerializer).serialize(serializableRow(row));
     }
 
     /**
@@ -527,7 +530,8 @@ Row serializableRow(Row row) {
       }
 
       if (schemaReflection.matchesAll(FieldMatcher.of(payloadKeyName, PAYLOAD_ROW_TYPE_NAME))) {
-        return row.getRow(payloadKeyName);
+        return checkArgumentNotNull(
+            row.getRow(payloadKeyName), "Payload field '%s' cannot be null", payloadKeyName);
       }
       Schema withUserFieldsOnly =
           removeFields(row.getSchema(), attributesKeyName, sourceTimestampKeyName);
@@ -553,8 +557,7 @@ static Builder builder() {
 
     abstract Field getTimestampField();
 
-    @Nullable
-    abstract Field getPayloadField();
+    abstract @Nullable Field getPayloadField();
 
     /**
      * Builds a {@link Schema} from {@link #getAttributesField()} and {@link #getTimestampField()}
@@ -565,8 +568,9 @@ Schema buildSchema(Field... additionalFields) {
       Schema.Builder builder =
           Schema.builder().addField(getAttributesField()).addField(getTimestampField());
 
-      if (getPayloadField() != null) {
-        builder = builder.addField(getPayloadField());
+      Field payloadField = getPayloadField();
+      if (payloadField != null) {
+        builder = builder.addField(payloadField);
       }
 
       for (Field field : additionalFields) {
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubSchemaIOProvider.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubSchemaIOProvider.java
index d39cee3ddc06..bcecdcc00280 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubSchemaIOProvider.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubSchemaIOProvider.java
@@ -24,6 +24,8 @@
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubMessageToRow.PAYLOAD_FIELD;
 import static org.apache.beam.sdk.io.gcp.pubsub.PubsubMessageToRow.TIMESTAMP_FIELD;
 import static org.apache.beam.sdk.schemas.Schema.TypeName.ROW;
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 
 import com.google.auto.service.AutoService;
 import com.google.auto.value.AutoValue;
@@ -97,9 +99,6 @@
  */
 @Internal
 @AutoService(SchemaIOProvider.class)
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubSchemaIOProvider implements SchemaIOProvider {
   public static final FieldType ATTRIBUTE_MAP_FIELD_TYPE =
       Schema.FieldType.map(FieldType.STRING.withNullable(false), FieldType.STRING);
@@ -137,11 +136,11 @@ public Schema configurationSchema() {
    * resides there, and some IO-specific configuration object.
    */
   @Override
-  public PubsubSchemaIO from(String location, Row configuration, Schema dataSchema) {
+  public PubsubSchemaIO from(String location, Row configuration, @Nullable Schema dataSchema) {
     validateConfigurationSchema(configuration);
-    validateDlq(configuration.getValue("deadLetterQueue"));
+    validateDlq(configuration.getString("deadLetterQueue"));
     validateDataSchema(dataSchema);
-    return new PubsubSchemaIO(location, configuration, dataSchema);
+    return new PubsubSchemaIO(location, configuration, checkArgumentNotNull(dataSchema));
   }
 
   @Override
@@ -154,7 +153,7 @@ public PCollection.IsBounded isBounded() {
     return PCollection.IsBounded.UNBOUNDED;
   }
 
-  private void validateDataSchema(Schema schema) {
+  private void validateDataSchema(@Nullable Schema schema) {
     if (schema == null) {
       throw new InvalidSchemaException(
           "Unsupported schema specified for Pubsub source in CREATE TABLE."
@@ -168,7 +167,7 @@ private void validateDataSchema(Schema schema) {
     }
   }
 
-  private void validateDlq(String deadLetterQueue) {
+  private void validateDlq(@Nullable String deadLetterQueue) {
     if (deadLetterQueue != null && deadLetterQueue.isEmpty()) {
       throw new InvalidConfigurationException("Dead letter queue topic name is not specified");
     }
@@ -252,7 +251,9 @@ public POutput expand(PCollection<Row> input) {
                     MapElements.into(TypeDescriptor.of(PubsubMessage.class))
                         .via(
                             row ->
-                                new PubsubMessage(serializer.serialize(row), ImmutableMap.of())));
+                                new PubsubMessage(
+                                    checkStateNotNull(serializer).serialize(row),
+                                    ImmutableMap.of())));
           } else {
             transformed =
                 filtered.apply(
@@ -268,33 +269,33 @@ private PubsubIO.Read<PubsubMessage> readMessagesWithAttributes() {
       PubsubIO.Read<PubsubMessage> read = PubsubIO.readMessagesWithAttributes().fromTopic(location);
 
       return config.useTimestampAttribute()
-          ? read.withTimestampAttribute(config.getTimestampAttributeKey())
+          ? read.withTimestampAttribute(checkStateNotNull(config.getTimestampAttributeKey()))
           : read;
     }
 
     private PubsubIO.Write<PubsubMessage> createPubsubMessageWrite() {
       PubsubIO.Write<PubsubMessage> write = PubsubIO.writeMessages().to(location);
       if (config.useTimestampAttribute()) {
-        write = write.withTimestampAttribute(config.getTimestampAttributeKey());
+        write = write.withTimestampAttribute(checkStateNotNull(config.getTimestampAttributeKey()));
       }
       return write;
     }
 
     private PubsubIO.Write<PubsubMessage> writeMessagesToDlq() {
       PubsubIO.Write<PubsubMessage> write =
-          PubsubIO.writeMessages().to(config.getDeadLetterQueue());
+          PubsubIO.writeMessages().to(checkStateNotNull(config.getDeadLetterQueue()));
 
       return config.useTimestampAttribute()
-          ? write.withTimestampAttribute(config.getTimestampAttributeKey())
+          ? write.withTimestampAttribute(checkStateNotNull(config.getTimestampAttributeKey()))
           : write;
     }
 
-    private boolean hasValidAttributesField(Schema schema) {
+    private static boolean hasValidAttributesField(Schema schema) {
       return fieldPresent(schema, ATTRIBUTES_FIELD, ATTRIBUTE_MAP_FIELD_TYPE)
           || fieldPresent(schema, ATTRIBUTES_FIELD, ATTRIBUTE_ARRAY_FIELD_TYPE);
     }
 
-    private boolean hasValidPayloadField(Schema schema) {
+    private static boolean hasValidPayloadField(Schema schema) {
       if (!schema.hasField(PAYLOAD_FIELD)) {
         return false;
       }
@@ -304,7 +305,7 @@ private boolean hasValidPayloadField(Schema schema) {
       return schema.getField(PAYLOAD_FIELD).getType().getTypeName().equals(ROW);
     }
 
-    private boolean shouldUseNestedSchema(Schema schema) {
+    private static boolean shouldUseNestedSchema(Schema schema) {
       return hasValidPayloadField(schema) && hasValidAttributesField(schema);
     }
 
@@ -350,16 +351,20 @@ boolean useTimestampAttribute() {
     }
 
     PayloadSerializer serializer(Schema schema) {
-      String format = getFormat() == null ? "json" : getFormat();
+      String configFormat = getFormat();
+      String format = configFormat == null ? "json" : configFormat;
       ImmutableMap.Builder<String, Object> params = ImmutableMap.builder();
-      if (getThriftClass() != null) {
-        params.put("thriftClass", getThriftClass());
+      String thriftClass = getThriftClass();
+      if (thriftClass != null) {
+        params.put("thriftClass", thriftClass);
       }
-      if (getThriftProtocolFactoryClass() != null) {
-        params.put("thriftProtocolFactoryClass", getThriftProtocolFactoryClass());
+      String thriftProtocolFactoryClass = getThriftProtocolFactoryClass();
+      if (thriftProtocolFactoryClass != null) {
+        params.put("thriftProtocolFactoryClass", thriftProtocolFactoryClass);
       }
-      if (getProtoClass() != null) {
-        params.put("protoClass", getProtoClass());
+      String protoClass = getProtoClass();
+      if (protoClass != null) {
+        params.put("protoClass", protoClass);
       }
       return PayloadSerializers.getSerializer(format, schema, params.build());
     }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubTestClient.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubTestClient.java
index 22fcaae20cad..ee320bb80889 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubTestClient.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubTestClient.java
@@ -17,6 +17,7 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
 
 import com.google.api.client.util.Clock;
@@ -40,9 +41,6 @@
  * testing {@link #publish}, {@link #pull}, {@link #acknowledge} and {@link #modifyAckDeadline}
  * methods. Relies on statics to mimic the Pubsub service, though we try to hide that.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubTestClient extends PubsubClient implements Serializable {
   /**
    * Mimic the state of the simulated Pubsub 'service'.
@@ -362,26 +360,28 @@ private static void setSchemaState(
   /** Handles verifying {@code STATE} at end of publish test. */
   private static void performFinalPublishStateChecks() {
     checkState(STATE.isActive, "No test still in flight");
+    Set<OutgoingMessage> remainingExpected =
+        checkStateNotNull(STATE.remainingExpectedOutgoingMessages);
     checkState(
-        STATE.remainingExpectedOutgoingMessages.isEmpty(),
+        remainingExpected.isEmpty(),
         "Still waiting for %s messages to be published",
-        STATE.remainingExpectedOutgoingMessages.size());
+        remainingExpected.size());
   }
 
   /** Handles verifying {@code STATE} at end of pull test. */
   private static void performFinalPullStateChecks() {
+    List<IncomingMessage> remainingPending =
+        checkStateNotNull(STATE.remainingPendingIncomingMessages);
+    Map<String, IncomingMessage> pendingAck = checkStateNotNull(STATE.pendingAckIncomingMessages);
+    Map<String, Long> ackDeadline = checkStateNotNull(STATE.ackDeadline);
     checkState(
-        STATE.remainingPendingIncomingMessages.isEmpty(),
+        remainingPending.isEmpty(),
         "Still waiting for %s messages to be pulled",
-        STATE.remainingPendingIncomingMessages.size());
+        remainingPending.size());
     checkState(
-        STATE.pendingAckIncomingMessages.isEmpty(),
-        "Still waiting for %s messages to be ACKed",
-        STATE.pendingAckIncomingMessages.size());
+        pendingAck.isEmpty(), "Still waiting for %s messages to be ACKed", pendingAck.size());
     checkState(
-        STATE.ackDeadline.isEmpty(),
-        "Still waiting for %s messages to be ACKed",
-        STATE.ackDeadline.size());
+        ackDeadline.isEmpty(), "Still waiting for %s messages to be ACKed", ackDeadline.size());
   }
 
   public static PubsubTestClientFactory createFactoryForCreateSubscription() {
@@ -445,13 +445,17 @@ private boolean inPublishMode() {
   public void advance() {
     synchronized (STATE) {
       checkState(inPullMode(), "Can only advance in pull mode");
+      Clock clock = checkStateNotNull(STATE.clock);
+      Map<String, Long> ackDeadline = checkStateNotNull(STATE.ackDeadline);
+      Map<String, IncomingMessage> pendingAck = checkStateNotNull(STATE.pendingAckIncomingMessages);
+      List<IncomingMessage> remainingPending =
+          checkStateNotNull(STATE.remainingPendingIncomingMessages);
       // Any messages who's ACKs timed out are available for re-pulling.
-      Iterator<Map.Entry<String, Long>> deadlineItr = STATE.ackDeadline.entrySet().iterator();
+      Iterator<Map.Entry<String, Long>> deadlineItr = ackDeadline.entrySet().iterator();
       while (deadlineItr.hasNext()) {
         Map.Entry<String, Long> entry = deadlineItr.next();
-        if (entry.getValue() <= STATE.clock.currentTimeMillis()) {
-          STATE.remainingPendingIncomingMessages.add(
-              STATE.pendingAckIncomingMessages.remove(entry.getKey()));
+        if (entry.getValue() <= clock.currentTimeMillis()) {
+          remainingPending.add(checkStateNotNull(pendingAck.remove(entry.getKey())));
           deadlineItr.remove();
         }
       }
@@ -465,14 +469,19 @@ public void close() {}
   public int publish(TopicPath topic, List<OutgoingMessage> outgoingMessages) throws IOException {
     synchronized (STATE) {
       checkState(inPublishMode(), "Can only publish in publish mode");
-      boolean isDynamic = STATE.expectedTopic == null;
+      TopicPath expectedTopic = STATE.expectedTopic;
+      boolean isDynamic = expectedTopic == null;
       if (!isDynamic) {
         checkState(
-            topic.equals(STATE.expectedTopic),
+            topic.equals(expectedTopic),
             "Topic %s does not match expected %s",
             topic,
-            STATE.expectedTopic);
+            expectedTopic);
       }
+      Set<OutgoingMessage> remainingExpected =
+          checkStateNotNull(STATE.remainingExpectedOutgoingMessages);
+      Set<OutgoingMessage> remainingFailing =
+          checkStateNotNull(STATE.remainingFailingOutgoingMessages);
       @MonotonicNonNull String batchOrderingKey = null;
       for (OutgoingMessage outgoingMessage : outgoingMessages) {
         if (batchOrderingKey == null) {
@@ -480,15 +489,15 @@ public int publish(TopicPath topic, List<OutgoingMessage> outgoingMessages) thro
         }
         checkState(outgoingMessage.getMessage().getOrderingKey().equals(batchOrderingKey));
         if (isDynamic) {
-          checkState(outgoingMessage.topic().equals(topic.getPath()));
+          checkState(topic.getPath().equals(outgoingMessage.topic()));
         } else {
           checkState(outgoingMessage.topic() == null);
         }
-        if (STATE.remainingFailingOutgoingMessages.remove(outgoingMessage)) {
+        if (remainingFailing.remove(outgoingMessage)) {
           throw new RuntimeException("Simulating failure for " + outgoingMessage);
         }
         checkState(
-            STATE.remainingExpectedOutgoingMessages.remove(outgoingMessage),
+            remainingExpected.remove(outgoingMessage),
             "Unexpected outgoing message %s",
             outgoingMessage);
       }
@@ -505,21 +514,27 @@ public List<IncomingMessage> pull(
       throws IOException {
     synchronized (STATE) {
       checkState(inPullMode(), "Can only pull in pull mode");
-      long now = STATE.clock.currentTimeMillis();
+      Clock clock = checkStateNotNull(STATE.clock);
+      long now = clock.currentTimeMillis();
       checkState(
           requestTimeMsSinceEpoch == now,
           "Simulated time %s does not match request time %s",
           now,
           requestTimeMsSinceEpoch);
+      SubscriptionPath expectedSubscription = checkStateNotNull(STATE.expectedSubscription);
       checkState(
-          subscription.equals(STATE.expectedSubscription),
+          subscription.equals(expectedSubscription),
           "Subscription %s does not match expected %s",
           subscription,
-          STATE.expectedSubscription);
+          expectedSubscription);
       checkState(returnImmediately, "Pull only supported if returning immediately");
 
       List<IncomingMessage> incomingMessages = new ArrayList<>();
-      Iterator<IncomingMessage> pendItr = STATE.remainingPendingIncomingMessages.iterator();
+      List<IncomingMessage> remainingPending =
+          checkStateNotNull(STATE.remainingPendingIncomingMessages);
+      Map<String, IncomingMessage> pendingAck = checkStateNotNull(STATE.pendingAckIncomingMessages);
+      Map<String, Long> ackDeadline = checkStateNotNull(STATE.ackDeadline);
+      Iterator<IncomingMessage> pendItr = remainingPending.iterator();
       while (pendItr.hasNext()) {
         IncomingMessage incomingMessage = pendItr.next();
         pendItr.remove();
@@ -531,9 +546,8 @@ public List<IncomingMessage> pull(
                 incomingMessage.ackId(),
                 incomingMessage.recordId());
         incomingMessages.add(incomingMessageWithRequestTime);
-        STATE.pendingAckIncomingMessages.put(
-            incomingMessageWithRequestTime.ackId(), incomingMessageWithRequestTime);
-        STATE.ackDeadline.put(
+        pendingAck.put(incomingMessageWithRequestTime.ackId(), incomingMessageWithRequestTime);
+        ackDeadline.put(
             incomingMessageWithRequestTime.ackId(),
             requestTimeMsSinceEpoch + STATE.ackTimeoutSec * 1000L);
         if (incomingMessages.size() >= batchSize) {
@@ -548,19 +562,22 @@ public List<IncomingMessage> pull(
   public void acknowledge(SubscriptionPath subscription, List<String> ackIds) throws IOException {
     synchronized (STATE) {
       checkState(inPullMode(), "Can only acknowledge in pull mode");
+      SubscriptionPath expectedSubscription = checkStateNotNull(STATE.expectedSubscription);
       checkState(
-          subscription.equals(STATE.expectedSubscription),
+          subscription.equals(expectedSubscription),
           "Subscription %s does not match expected %s",
           subscription,
-          STATE.expectedSubscription);
+          expectedSubscription);
 
+      Map<String, Long> ackDeadline = checkStateNotNull(STATE.ackDeadline);
+      Map<String, IncomingMessage> pendingAck = checkStateNotNull(STATE.pendingAckIncomingMessages);
       for (String ackId : ackIds) {
         checkState(
-            STATE.ackDeadline.remove(ackId) != null,
+            ackDeadline.remove(ackId) != null,
             "No message with ACK id %s is waiting for an ACK",
             ackId);
         checkState(
-            STATE.pendingAckIncomingMessages.remove(ackId) != null,
+            pendingAck.remove(ackId) != null,
             "No message with ACK id %s is waiting for an ACK",
             ackId);
       }
@@ -572,31 +589,40 @@ public void modifyAckDeadline(
       SubscriptionPath subscription, List<String> ackIds, int deadlineSeconds) throws IOException {
     synchronized (STATE) {
       checkState(inPullMode(), "Can only modify ack deadline in pull mode");
+      SubscriptionPath expectedSubscription = checkStateNotNull(STATE.expectedSubscription);
       checkState(
-          subscription.equals(STATE.expectedSubscription),
+          subscription.equals(expectedSubscription),
           "Subscription %s does not match expected %s",
           subscription,
-          STATE.expectedSubscription);
+          expectedSubscription);
 
+      Map<String, Long> ackDeadline = checkStateNotNull(STATE.ackDeadline);
+      Map<String, IncomingMessage> pendingAck = checkStateNotNull(STATE.pendingAckIncomingMessages);
+      Clock clock = checkStateNotNull(STATE.clock);
+      List<IncomingMessage> remainingPending =
+          checkStateNotNull(STATE.remainingPendingIncomingMessages);
       for (String ackId : ackIds) {
         if (deadlineSeconds > 0) {
           checkState(
-              STATE.ackDeadline.remove(ackId) != null,
+              ackDeadline.remove(ackId) != null,
               "No message with ACK id %s is waiting for an ACK",
               ackId);
           checkState(
-              STATE.pendingAckIncomingMessages.containsKey(ackId),
+              pendingAck.containsKey(ackId),
               "No message with ACK id %s is waiting for an ACK",
               ackId);
-          STATE.ackDeadline.put(ackId, STATE.clock.currentTimeMillis() + deadlineSeconds * 1000L);
+          ackDeadline.put(ackId, clock.currentTimeMillis() + deadlineSeconds * 1000L);
         } else {
           checkState(
-              STATE.ackDeadline.remove(ackId) != null,
+              ackDeadline.remove(ackId) != null,
               "No message with ACK id %s is waiting for an ACK",
               ackId);
-          IncomingMessage message = STATE.pendingAckIncomingMessages.remove(ackId);
-          checkState(message != null, "No message with ACK id %s is waiting for an ACK", ackId);
-          STATE.remainingPendingIncomingMessages.add(message);
+          IncomingMessage message =
+              checkStateNotNull(
+                  pendingAck.remove(ackId),
+                  "No message with ACK id %s is waiting for an ACK",
+                  ackId);
+          remainingPending.add(message);
         }
       }
     }
@@ -656,7 +682,7 @@ public int ackDeadlineSeconds(SubscriptionPath subscription) throws IOException
   public boolean isEOF() {
     synchronized (STATE) {
       checkState(inPullMode(), "Can only check EOF in pull mode");
-      return STATE.remainingPendingIncomingMessages.isEmpty();
+      return checkStateNotNull(STATE.remainingPendingIncomingMessages).isEmpty();
     }
   }
 
@@ -674,12 +700,12 @@ public void deleteSchema(SchemaPath schemaPath) throws IOException {
   }
 
   @Override
-  public SchemaPath getSchemaPath(TopicPath topicPath) throws IOException {
+  public @Nullable SchemaPath getSchemaPath(TopicPath topicPath) throws IOException {
     return STATE.expectedSchemaPath;
   }
 
   @Override
   public Schema getSchema(SchemaPath schemaPath) throws IOException {
-    return STATE.expectedSchema;
+    return checkStateNotNull(STATE.expectedSchema, "expectedSchema is not set");
   }
 }
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSink.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSink.java
index 3fe7d51aec1e..45c0b329988d 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSink.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSink.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
 
 import com.google.protobuf.InvalidProtocolBufferException;
@@ -96,9 +98,6 @@
  *       dedup messages.
  * </ul>
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubUnboundedSink extends PTransform<PCollection<PubsubMessage>, PDone> {
   /** Default maximum number of messages per publish. */
   static final int DEFAULT_PUBLISH_BATCH_SIZE = 1000;
@@ -109,7 +108,6 @@ public class PubsubUnboundedSink extends PTransform<PCollection<PubsubMessage>,
   /** Default longest delay between receiving a message and pushing it to Pubsub. */
   private static final Duration DEFAULT_MAX_LATENCY = Duration.standardSeconds(2);
 
-  /** Coder for conveying outgoing messages between internal stages. */
   /** Coder for conveying outgoing messages between internal stages. */
   private static class OutgoingMessageCoder extends AtomicCoder<OutgoingMessage> {
     private static final NullableCoder<String> RECORD_ID_CODER =
@@ -198,7 +196,7 @@ public void processElement(
           recordId = Hashing.murmur3_128().hashBytes(elementBytes).toString();
           break;
         case RANDOM:
-          // Since these elements go through a GroupByKey, any  failures while sending to
+          // Since these elements go through a GroupByKey, any failures while sending to
           // Pubsub will be retried without falling back and generating a new record id.
           // Thus even though we may send the same message to Pubsub twice, it is guaranteed
           // to have the same record id.
@@ -246,11 +244,11 @@ private static class OutgoingData {
 
     private final PubsubClientFactory pubsubFactory;
     private final @Nullable ValueProvider<TopicPath> topic;
-    private final String timestampAttribute;
-    private final String idAttribute;
+    private final @Nullable String timestampAttribute;
+    private final @Nullable String idAttribute;
     private final int publishBatchBytes;
 
-    private final String pubsubRootUrl;
+    private final @Nullable String pubsubRootUrl;
 
     /** Client on which to talk to Pubsub. Null until created by {@link #startBundle}. */
     private transient @Nullable PubsubClient pubsubClient;
@@ -262,8 +260,8 @@ private static class OutgoingData {
     WriterFn(
         PubsubClientFactory pubsubFactory,
         @Nullable ValueProvider<TopicPath> topic,
-        String timestampAttribute,
-        String idAttribute,
+        @Nullable String timestampAttribute,
+        @Nullable String idAttribute,
         int publishBatchSize,
         int publishBatchBytes) {
       this.pubsubFactory = pubsubFactory;
@@ -277,10 +275,10 @@ private static class OutgoingData {
     WriterFn(
         PubsubClientFactory pubsubFactory,
         @Nullable ValueProvider<TopicPath> topic,
-        String timestampAttribute,
-        String idAttribute,
+        @Nullable String timestampAttribute,
+        @Nullable String idAttribute,
         int publishBatchBytes,
-        String pubsubRootUrl) {
+        @Nullable String pubsubRootUrl) {
       this.pubsubFactory = pubsubFactory;
       this.topic = topic;
       this.timestampAttribute = timestampAttribute;
@@ -290,11 +288,13 @@ private static class OutgoingData {
     }
 
     @VisibleForTesting
+    @Nullable
     String getIdAttribute() {
       return idAttribute;
     }
 
     @VisibleForTesting
+    @Nullable
     ValueProvider<TopicPath> getTopic() {
       return topic;
     }
@@ -308,11 +308,9 @@ private void publishBatch(List<OutgoingMessage> messages, int bytes) throws IOEx
       } else {
         // This is the dynamic topic destinations case. Since we first group by topic, we can assume
         // that all messages in the batch have the same topic.
-        topicPath =
-            PubsubClient.topicPathFromPath(
-                org.apache.beam.sdk.util.Preconditions.checkStateNotNull(messages.get(0).topic()));
+        topicPath = PubsubClient.topicPathFromPath(checkStateNotNull(messages.get(0).topic()));
       }
-      int n = pubsubClient.publish(topicPath, messages);
+      int n = checkStateNotNull(pubsubClient).publish(topicPath, messages);
       checkState(
           n == messages.size(),
           "Attempted to publish %s messages but %s were successful",
@@ -380,8 +378,11 @@ public void processElement(ProcessContext c) throws Exception {
 
     @FinishBundle
     public void finishBundle() throws Exception {
-      pubsubClient.close();
-      pubsubClient = null;
+      final PubsubClient pubsubClient = this.pubsubClient;
+      if (pubsubClient != null) {
+        pubsubClient.close();
+      }
+      this.pubsubClient = null;
     }
 
     @Override
@@ -448,21 +449,21 @@ public void populateDisplayData(DisplayData.Builder builder) {
    */
   private final RecordIdMethod recordIdMethod;
 
-  private final String pubsubRootUrl;
+  private final @Nullable String pubsubRootUrl;
 
   @VisibleForTesting
   PubsubUnboundedSink(
       PubsubClientFactory pubsubFactory,
       @Nullable ValueProvider<TopicPath> topic,
-      String timestampAttribute,
-      String idAttribute,
+      @Nullable String timestampAttribute,
+      @Nullable String idAttribute,
       int numShards,
       boolean publishBatchWithOrderingKey,
       int publishBatchSize,
       int publishBatchBytes,
       Duration maxLatency,
       RecordIdMethod recordIdMethod,
-      String pubsubRootUrl) {
+      @Nullable String pubsubRootUrl) {
     this.pubsubFactory = pubsubFactory;
     this.topic = topic;
     this.timestampAttribute = timestampAttribute;
@@ -544,14 +545,14 @@ public PubsubUnboundedSink(
 
   public PubsubUnboundedSink(
       PubsubClientFactory pubsubFactory,
-      ValueProvider<TopicPath> topic,
-      String timestampAttribute,
-      String idAttribute,
+      @Nullable ValueProvider<TopicPath> topic,
+      @Nullable String timestampAttribute,
+      @Nullable String idAttribute,
       int numShards,
       boolean publishBatchWithOrderingKey,
       int publishBatchSize,
       int publishBatchBytes,
-      String pubsubRootUrl) {
+      @Nullable String pubsubRootUrl) {
     this(
         pubsubFactory,
         topic,
@@ -604,7 +605,12 @@ public PDone expand(PCollection<PubsubMessage> input) {
       return input
           .apply(
               "WithDynamicTopics",
-              WithKeys.of(PubsubMessage::getTopic).withKeyType(TypeDescriptors.strings()))
+              WithKeys.of(
+                      (PubsubMessage msg) ->
+                          checkArgumentNotNull(
+                              msg.getTopic(),
+                              "Topic must be set on PubsubMessage when writing to dynamic topics."))
+                  .withKeyType(TypeDescriptors.strings()))
           .apply(
               MapValues.into(new TypeDescriptor<byte[]>() {})
                   .via(new PubsubMessages.ParsePayloadAsPubsubMessageProto()))
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSource.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSource.java
index bc91e9f381d4..a6f3917b0d59 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSource.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubUnboundedSource.java
@@ -17,6 +17,7 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkArgument;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
@@ -114,9 +115,6 @@
  *       UnboundedSource.UnboundedReader} instances to execute concurrently and thus hide latency.
  * </ul>
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class PubsubUnboundedSource extends PTransform<PBegin, PCollection<PubsubMessage>> {
   private static final Logger LOG = LoggerFactory.getLogger(PubsubUnboundedSource.class);
 
@@ -265,12 +263,18 @@ public PubsubCheckpoint(
      */
     @Override
     public void finalizeCheckpoint() throws IOException {
-      checkState(reader != null && safeToAckIds != null, "Cannot finalize a restored checkpoint");
-      // Even if the 'true' active reader has changed since the checkpoint was taken we are
+      final PubsubReader reader =
+          checkStateNotNull(this.reader, "Cannot finalize a restored checkpoint");
+      final List<String> safeToAckIds =
+          checkStateNotNull(this.safeToAckIds, "Cannot finalize a restored checkpoint");
+      // Even if the 'true' active reader has changed since the checkpoint was taken
+      // we are
       // fine:
-      // - The underlying Pubsub topic will not have changed, so the following ACKs will still
+      // - The underlying Pubsub topic will not have changed, so the following ACKs
+      // will still
       // go to the right place.
-      // - We'll delete the ACK ids from the readers in-flight state, but that only effects
+      // - We'll delete the ACK ids from the readers in-flight state, but that only
+      // effects
       // flow control and stats, neither of which are relevant anymore.
       try {
         int n = safeToAckIds.size();
@@ -291,8 +295,8 @@ public void finalizeCheckpoint() throws IOException {
         int remainingInFlight = reader.numInFlightCheckpoints.decrementAndGet();
         checkState(remainingInFlight >= 0, "Miscounted in-flight checkpoints");
         reader.maybeCloseClient();
-        reader = null;
-        safeToAckIds = null;
+        this.reader = null;
+        this.safeToAckIds = null;
       }
     }
 
@@ -330,7 +334,7 @@ public void nackAll(PubsubReader reader) throws IOException {
 
   /** The coder for our checkpoints. */
   private static class PubsubCheckpointCoder<T> extends AtomicCoder<PubsubCheckpoint> {
-    private static final Coder<String> SUBSCRIPTION_PATH_CODER =
+    private static final Coder<@Nullable String> SUBSCRIPTION_PATH_CODER =
         NullableCoder.of(StringUtf8Coder.of());
     private static final Coder<List<String>> LIST_CODER = ListCoder.of(StringUtf8Coder.of());
 
@@ -348,7 +352,7 @@ public void encode(PubsubCheckpoint value, OutputStream outStream) throws IOExce
 
     @Override
     public PubsubCheckpoint decode(InputStream inStream) throws IOException {
-      String path = SUBSCRIPTION_PATH_CODER.decode(inStream);
+      @Nullable String path = SUBSCRIPTION_PATH_CODER.decode(inStream);
       List<String> notYetReadIds = LIST_CODER.decode(inStream);
       return new PubsubCheckpoint(path, null, null, notYetReadIds);
     }
@@ -370,13 +374,13 @@ static class PubsubReader extends UnboundedSource.UnboundedReader<byte[]> {
     @VisibleForTesting final SubscriptionPath subscription;
 
     /** Client on which to talk to Pubsub. Contains a null value if the client has been closed. */
-    private AtomicReference<PubsubClient> pubsubClient;
+    private final AtomicReference<@Nullable PubsubClient> pubsubClient;
 
     /**
      * The closed state of this {@link PubsubReader}. If true, the reader has not yet been closed,
      * and it will have a non-null value within {@link #pubsubClient}.
      */
-    private AtomicBoolean active = new AtomicBoolean(true);
+    private final AtomicBoolean active = new AtomicBoolean(true);
 
     /**
      * Ack timeout, in ms, as set on subscription when we first start reading. Not updated
@@ -385,7 +389,7 @@ static class PubsubReader extends UnboundedSource.UnboundedReader<byte[]> {
     private int ackTimeoutMs;
 
     /** ACK ids of messages we have delivered downstream but not yet ACKed. */
-    private Set<String> safeToAckIds;
+    private final Set<String> safeToAckIds;
 
     /**
      * Messages we have received from Pubsub and not yet delivered downstream. We preserve their
@@ -427,13 +431,13 @@ public InFlightState(long requestTimeMsSinceEpoch, long ackDeadlineMsSinceEpoch)
      * Bucketed map from received time (as system time, ms since epoch) to message timestamps
      * (mssince epoch) of all received but not-yet read messages. Used to estimate watermark.
      */
-    private BucketingFunction minUnreadTimestampMsSinceEpoch;
+    private final BucketingFunction minUnreadTimestampMsSinceEpoch;
 
     /**
      * Minimum of timestamps (ms since epoch) of all recently read messages. Used to estimate
      * watermark.
      */
-    private MovingFunction minReadTimestampMsSinceEpoch;
+    private final MovingFunction minReadTimestampMsSinceEpoch;
 
     /**
      * System time (ms since epoch) we last received a message from Pubsub, or -1 if not yet
@@ -454,60 +458,60 @@ public InFlightState(long requestTimeMsSinceEpoch, long ackDeadlineMsSinceEpoch)
     private long numReceived;
 
     /** Stats only: Number of messages which have recently been received. */
-    private MovingFunction numReceivedRecently;
+    private final MovingFunction numReceivedRecently;
 
     /** Stats only: Number of messages which have recently had their deadline extended. */
-    private MovingFunction numExtendedDeadlines;
+    private final MovingFunction numExtendedDeadlines;
 
     /**
      * Stats only: Number of messages which have recenttly had their deadline extended even though
      * it may be too late to do so.
      */
-    private MovingFunction numLateDeadlines;
+    private final MovingFunction numLateDeadlines;
 
     /** Stats only: Number of messages which have recently been ACKed. */
-    private MovingFunction numAcked;
+    private final MovingFunction numAcked;
 
     /**
      * Stats only: Number of messages which have recently expired (ACKs were extended for too long).
      */
-    private MovingFunction numExpired;
+    private final MovingFunction numExpired;
 
     /** Stats only: Number of messages which have recently been NACKed. */
-    private MovingFunction numNacked;
+    private final MovingFunction numNacked;
 
     /** Stats only: Number of message bytes which have recently been read by downstream consumer. */
-    private MovingFunction numReadBytes;
+    private final MovingFunction numReadBytes;
 
     /**
      * Stats only: Minimum of timestamp (ms since epoch) of all recently received messages. Used to
-     * estimate timestamp skew. Does not contribute to watermark estimator.
+     * estimate timestamp skew. Does not contribute to watermark watermark.
      */
-    private MovingFunction minReceivedTimestampMsSinceEpoch;
+    private final MovingFunction minReceivedTimestampMsSinceEpoch;
 
     /**
      * Stats only: Maximum of timestamp (ms since epoch) of all recently received messages. Used to
      * estimate timestamp skew.
      */
-    private MovingFunction maxReceivedTimestampMsSinceEpoch;
+    private final MovingFunction maxReceivedTimestampMsSinceEpoch;
 
     /** Stats only: Minimum of recent estimated watermarks (ms since epoch). */
-    private MovingFunction minWatermarkMsSinceEpoch;
+    private final MovingFunction minWatermarkMsSinceEpoch;
 
     /** Stats ony: Maximum of recent estimated watermarks (ms since epoch). */
-    private MovingFunction maxWatermarkMsSinceEpoch;
+    private final MovingFunction maxWatermarkMsSinceEpoch;
 
     /**
      * Stats only: Number of messages with timestamps strictly behind the estimated watermark at the
      * time they are received. These may be considered 'late' by downstream computations.
      */
-    private MovingFunction numLateMessages;
+    private final MovingFunction numLateMessages;
 
     /**
      * Stats only: Current number of checkpoints in flight. CAUTION: Accessed by both checkpointing
      * and reader threads.
      */
-    private AtomicInteger numInFlightCheckpoints;
+    private final AtomicInteger numInFlightCheckpoints;
 
     /** Stats only: Maximum number of checkpoints in flight at any time. */
     private int maxInFlightCheckpoints;
@@ -563,7 +567,11 @@ public PubsubReader(PubsubOptions options, PubsubSource outer, SubscriptionPath
 
     @VisibleForTesting
     PubsubClient getPubsubClient() {
-      return pubsubClient.get();
+      return getClient();
+    }
+
+    private PubsubClient getClient() {
+      return checkStateNotNull(pubsubClient.get(), "Client has been closed");
     }
 
     /**
@@ -575,7 +583,7 @@ PubsubClient getPubsubClient() {
      * <p>CAUTION: Retains {@code ackIds}.
      */
     void ackBatch(List<String> ackIds) throws IOException {
-      pubsubClient.get().acknowledge(subscription, ackIds);
+      getClient().acknowledge(subscription, ackIds);
       ackedIds.add(ackIds);
     }
 
@@ -584,7 +592,7 @@ void ackBatch(List<String> ackIds) throws IOException {
      * given {@code ackIds}. Does not retain {@code ackIds}.
      */
     public void nackBatch(long nowMsSinceEpoch, List<String> ackIds) throws IOException {
-      pubsubClient.get().modifyAckDeadline(subscription, ackIds, 0);
+      getClient().modifyAckDeadline(subscription, ackIds, 0);
       numNacked.add(nowMsSinceEpoch, ackIds.size());
     }
 
@@ -594,7 +602,7 @@ public void nackBatch(long nowMsSinceEpoch, List<String> ackIds) throws IOExcept
      */
     private void extendBatch(long nowMsSinceEpoch, List<String> ackIds) throws IOException {
       int extensionSec = (ackTimeoutMs * ACK_EXTENSION_PCT) / (100 * 1000);
-      pubsubClient.get().modifyAckDeadline(subscription, ackIds, extensionSec);
+      getClient().modifyAckDeadline(subscription, ackIds, extensionSec);
       numExtendedDeadlines.add(nowMsSinceEpoch, ackIds.size());
     }
 
@@ -648,7 +656,8 @@ private void extend() throws IOException {
               < nowMsSinceEpoch) {
             // Pubsub may have already considered this message to have expired.
             // If so it will (eventually) be made available on a future pull request.
-            // If this message ends up being committed then it will be considered a duplicate
+            // If this message ends up being committed then it will be considered a
+            // duplicate
             // when re-pulled.
             assumeExpired.add(entry.getKey());
             continue;
@@ -693,11 +702,12 @@ private void extend() throws IOException {
 
         if (!toBeExtended.isEmpty()) {
           // Pubsub extends acks from it's notion of current time.
-          // We'll try to track that on our side, but note the deadlines won't necessarily agree.
+          // We'll try to track that on our side, but note the deadlines won't necessarily
+          // agree.
           long newDeadlineMsSinceEpoch = nowMsSinceEpoch + (ackTimeoutMs * ACK_EXTENSION_PCT) / 100;
           for (String ackId : toBeExtended) {
             // Maintain increasing ack deadline order.
-            InFlightState state = inFlight.remove(ackId);
+            InFlightState state = checkStateNotNull(inFlight.remove(ackId));
             inFlight.put(
                 ackId, new InFlightState(state.requestTimeMsSinceEpoch, newDeadlineMsSinceEpoch));
           }
@@ -711,8 +721,10 @@ private void extend() throws IOException {
     private void pull() throws IOException {
       if (inFlight.size() >= MAX_IN_FLIGHT) {
         // Wait for checkpoint to be finalized before pulling anymore.
-        // There may be lag while checkpoints are persisted and the finalizeCheckpoint method
-        // is invoked. By limiting the in-flight messages we can ensure we don't end up consuming
+        // There may be lag while checkpoints are persisted and the finalizeCheckpoint
+        // method
+        // is invoked. By limiting the in-flight messages we can ensure we don't end up
+        // consuming
         // messages faster than we can checkpoint them.
         return;
       }
@@ -723,7 +735,7 @@ private void pull() throws IOException {
       // Pull the next batch.
       // BLOCKs until received.
       Collection<PubsubClient.IncomingMessage> receivedMessages =
-          pubsubClient.get().pull(requestTimeMsSinceEpoch, subscription, PULL_BATCH_SIZE, true);
+          getClient().pull(requestTimeMsSinceEpoch, subscription, PULL_BATCH_SIZE, true);
       if (receivedMessages.isEmpty()) {
         // Nothing available yet. Try again later.
         return;
@@ -779,7 +791,8 @@ private void stats() {
       String oldestAckId = Iterables.getFirst(inFlight.keySet(), null);
       if (oldestAckId != null) {
         oldestInFlight =
-            (nowMsSinceEpoch - inFlight.get(oldestAckId).requestTimeMsSinceEpoch) + "ms";
+            (nowMsSinceEpoch - checkStateNotNull(inFlight.get(oldestAckId)).requestTimeMsSinceEpoch)
+                + "ms";
       }
 
       LOG.debug(
@@ -828,7 +841,7 @@ private void stats() {
     @Override
     public boolean start() throws IOException {
       // Determine the ack timeout.
-      ackTimeoutMs = pubsubClient.get().ackDeadlineSeconds(subscription) * 1000;
+      ackTimeoutMs = getClient().ackDeadlineSeconds(subscription) * 1000;
       return advance();
     }
 
@@ -843,7 +856,8 @@ public boolean advance() throws IOException {
       stats();
 
       if (current != null) {
-        // Current is consumed. It can no longer contribute to holding back the watermark.
+        // Current is consumed. It can no longer contribute to holding back the
+        // watermark.
         minUnreadTimestampMsSinceEpoch.remove(current.requestTimeMsSinceEpoch());
         current = null;
       }
@@ -853,24 +867,28 @@ public boolean advance() throws IOException {
 
       // Extend all pressing deadlines.
       // Will BLOCK until done.
-      // If the system is pulling messages only to let them sit in a downsteam queue then
+      // If the system is pulling messages only to let them sit in a downsteam queue
+      // then
       // this will have the effect of slowing down the pull rate.
-      // However, if the system is genuinely taking longer to process each message then
+      // However, if the system is genuinely taking longer to process each message
+      // then
       // the work to extend ACKs would be better done in the background.
       extend();
 
       if (notYetRead.isEmpty()) {
         // Pull another batch.
-        // Will BLOCK until fetch returns, but will not block until a message is available.
+        // Will BLOCK until fetch returns, but will not block until a message is
+        // available.
         pull();
       }
 
       // Take one message from queue.
-      current = notYetRead.poll();
+      final PubsubClient.@Nullable IncomingMessage current = notYetRead.poll();
       if (current == null) {
         // Try again later.
         return false;
       }
+      this.current = current;
       notYetReadBytes -= current.message().getData().size();
       checkState(notYetReadBytes >= 0);
       long nowMsSinceEpoch = now();
@@ -888,6 +906,7 @@ public boolean advance() throws IOException {
 
     @Override
     public byte[] getCurrent() throws NoSuchElementException {
+      final PubsubClient.@Nullable IncomingMessage current = this.current;
       if (current == null) {
         throw new NoSuchElementException();
       }
@@ -901,6 +920,7 @@ public byte[] getCurrent() throws NoSuchElementException {
 
     @Override
     public Instant getCurrentTimestamp() throws NoSuchElementException {
+      final PubsubClient.@Nullable IncomingMessage current = this.current;
       if (current == null) {
         throw new NoSuchElementException();
       }
@@ -909,6 +929,7 @@ public Instant getCurrentTimestamp() throws NoSuchElementException {
 
     @Override
     public byte[] getCurrentRecordId() throws NoSuchElementException {
+      final PubsubClient.@Nullable IncomingMessage current = this.current;
       if (current == null) {
         throw new NoSuchElementException();
       }
@@ -934,7 +955,8 @@ public void close() throws IOException {
      */
     private void maybeCloseClient() throws IOException {
       if (!active.get() && numInFlightCheckpoints.get() == 0) {
-        // The reader has been closed and it has no more outstanding checkpoints. The client
+        // The reader has been closed and it has no more outstanding checkpoints. The
+        // client
         // must be closed so it doesn't leak
         PubsubClient client = pubsubClient.getAndSet(null);
         if (client != null) {
@@ -950,18 +972,23 @@ public PubsubSource getCurrentSource() {
 
     @Override
     public Instant getWatermark() {
-      if (pubsubClient.get().isEOF() && notYetRead.isEmpty()) {
+      if (getClient().isEOF() && notYetRead.isEmpty()) {
         // For testing only: Advance the watermark to the end of time to signal
         // the test is complete.
         return BoundedWindow.TIMESTAMP_MAX_VALUE;
       }
 
-      // NOTE: We'll allow the watermark to go backwards. The underlying runner is responsible
-      // for aggregating all reported watermarks and ensuring the aggregate is latched.
-      // If we attempt to latch locally then it is possible a temporary starvation of one reader
-      // could cause its estimated watermark to fast forward to current system time. Then when
+      // NOTE: We'll allow the watermark to go backwards. The underlying runner is
+      // responsible
+      // for aggregating all reported watermarks and ensuring the aggregate is
+      // latched.
+      // If we attempt to latch locally then it is possible a temporary starvation of
+      // one reader
+      // could cause its estimated watermark to fast forward to current system time.
+      // Then when
       // the reader resumes its watermark would be unable to resume tracking.
-      // By letting the underlying runner latch we avoid any problems due to localized starvation.
+      // By letting the underlying runner latch we avoid any problems due to localized
+      // starvation.
       long nowMsSinceEpoch = now();
       long readMin = minReadTimestampMsSinceEpoch.get(nowMsSinceEpoch);
       long unreadMin = minUnreadTimestampMsSinceEpoch.get();
@@ -969,17 +996,21 @@ public Instant getWatermark() {
           && unreadMin == Long.MAX_VALUE
           && lastReceivedMsSinceEpoch >= 0
           && nowMsSinceEpoch > lastReceivedMsSinceEpoch + SAMPLE_PERIOD.getMillis()) {
-        // We don't currently have any unread messages pending, we have not had any messages
-        // read for a while, and we have not received any new messages from Pubsub for a while.
+        // We don't currently have any unread messages pending, we have not had any
+        // messages
+        // read for a while, and we have not received any new messages from Pubsub for a
+        // while.
         // Advance watermark to current time.
         // TODO: Estimate a timestamp lag.
         lastWatermarkMsSinceEpoch = nowMsSinceEpoch;
       } else if (minReadTimestampMsSinceEpoch.isSignificant()
           || minUnreadTimestampMsSinceEpoch.isSignificant()) {
-        // Take minimum of the timestamps in all unread messages and recently read messages.
+        // Take minimum of the timestamps in all unread messages and recently read
+        // messages.
         lastWatermarkMsSinceEpoch = Math.min(readMin, unreadMin);
       }
-      // else: We're not confident enough to estimate a new watermark. Stick with the old one.
+      // else: We're not confident enough to estimate a new watermark. Stick with the
+      // old one.
       minWatermarkMsSinceEpoch.add(nowMsSinceEpoch, lastWatermarkMsSinceEpoch);
       maxWatermarkMsSinceEpoch.add(nowMsSinceEpoch, lastWatermarkMsSinceEpoch);
       return new Instant(lastWatermarkMsSinceEpoch);
@@ -991,15 +1022,18 @@ public PubsubCheckpoint getCheckpointMark() {
       maxInFlightCheckpoints = Math.max(maxInFlightCheckpoints, cur);
       // It's possible for a checkpoint to be taken but never finalized.
       // So we simply copy whatever safeToAckIds we currently have.
-      // It's possible a later checkpoint will be taken before an earlier one is finalized,
-      // in which case we'll double ACK messages to Pubsub. However Pubsub is fine with that.
+      // It's possible a later checkpoint will be taken before an earlier one is
+      // finalized,
+      // in which case we'll double ACK messages to Pubsub. However Pubsub is fine
+      // with that.
       List<String> snapshotSafeToAckIds = Lists.newArrayList(safeToAckIds);
       List<String> snapshotNotYetReadIds = new ArrayList<>(notYetRead.size());
       for (PubsubClient.IncomingMessage incomingMessage : notYetRead) {
         snapshotNotYetReadIds.add(incomingMessage.ackId());
       }
       if (outer.subscriptionPath == null) {
-        // need to include the subscription in case we resume, as it's not stored in the source.
+        // need to include the subscription in case we resume, as it's not stored in the
+        // source.
         return new PubsubCheckpoint(
             subscription.getPath(), this, snapshotSafeToAckIds, snapshotNotYetReadIds);
       }
@@ -1020,14 +1054,14 @@ public long getSplitBacklogBytes() {
   static class PubsubSource extends UnboundedSource<byte[], PubsubCheckpoint> {
     public final PubsubUnboundedSource outer;
     // The subscription to read from.
-    @VisibleForTesting final ValueProvider<SubscriptionPath> subscriptionPath;
+    @VisibleForTesting final @Nullable ValueProvider<SubscriptionPath> subscriptionPath;
 
     public PubsubSource(PubsubUnboundedSource outer) {
       this(outer, outer.getSubscriptionProvider());
     }
 
     private PubsubSource(
-        PubsubUnboundedSource outer, ValueProvider<SubscriptionPath> subscriptionPath) {
+        PubsubUnboundedSource outer, @Nullable ValueProvider<SubscriptionPath> subscriptionPath) {
       this.outer = outer;
       this.subscriptionPath = subscriptionPath;
     }
@@ -1055,16 +1089,22 @@ public PubsubReader createReader(
         PipelineOptions options, @Nullable PubsubCheckpoint checkpoint) {
       PubsubReader reader;
       SubscriptionPath subscription;
-      if (subscriptionPath == null || subscriptionPath.get() == null) {
+      final @Nullable ValueProvider<SubscriptionPath> subscriptionPath = this.subscriptionPath;
+      final @Nullable SubscriptionPath subscriptionPathVal =
+          subscriptionPath == null ? null : subscriptionPath.get();
+      if (subscriptionPathVal == null) {
         if (checkpoint == null) {
           // This reader has never been started and there was no call to #split;
           // create a single random subscription, which will be kept in the checkpoint.
           subscription = outer.createRandomSubscription(options);
         } else {
-          subscription = checkpoint.getSubscription();
+          subscription =
+              checkStateNotNull(
+                  checkpoint.getSubscription(),
+                  "Checkpoint must have a subscription path when subscriptionPath is not set.");
         }
       } else {
-        subscription = subscriptionPath.get();
+        subscription = subscriptionPathVal;
       }
       try {
         reader = new PubsubReader(options.as(PubsubOptions.class), this, subscription);
@@ -1088,7 +1128,7 @@ public PubsubReader createReader(
     }
 
     @Override
-    public @Nullable Coder<PubsubCheckpoint> getCheckpointMarkCoder() {
+    public Coder<PubsubCheckpoint> getCheckpointMarkCoder() {
       return CHECKPOINT_CODER;
     }
 
@@ -1104,7 +1144,8 @@ public void validate() {
 
     @Override
     public boolean requiresDeduping() {
-      // We cannot prevent re-offering already read messages after a restore from checkpoint.
+      // We cannot prevent re-offering already read messages after a restore from
+      // checkpoint.
       return true;
     }
   }
@@ -1205,7 +1246,7 @@ public void populateDisplayData(DisplayData.Builder builder) {
 
   @VisibleForTesting
   PubsubUnboundedSource(
-      Clock clock,
+      @Nullable Clock clock,
       PubsubClientFactory pubsubFactory,
       @Nullable ValueProvider<ProjectPath> project,
       @Nullable ValueProvider<TopicPath> topic,
@@ -1254,7 +1295,7 @@ public PubsubUnboundedSource(
 
   /** Construct an unbounded source to consume from the Pubsub {@code subscription}. */
   public PubsubUnboundedSource(
-      Clock clock,
+      @Nullable Clock clock,
       PubsubClientFactory pubsubFactory,
       @Nullable ValueProvider<ProjectPath> project,
       @Nullable ValueProvider<TopicPath> topic,
@@ -1400,18 +1441,21 @@ private boolean usesStatsFn(PipelineOptions options) {
   }
 
   private SubscriptionPath createRandomSubscription(PipelineOptions options) {
-    TopicPath topicPath = topic.get();
+    TopicPath topicPath =
+        checkStateNotNull(
+            checkStateNotNull(topic, "Topic must be set to create a random subscription").get(),
+            "Topic value must be set to create a random subscription");
 
     ProjectPath projectPath;
     if (project != null) {
-      projectPath = project.get();
+      projectPath = checkStateNotNull(project.get(), "Project value must be set");
     } else {
       String projectId = options.as(GcpOptions.class).getProject();
       checkState(
           projectId != null,
           "Cannot create subscription to topic %s because pipeline option 'project' not specified",
           topicPath);
-      projectPath = PubsubClient.projectPathFromId(options.as(GcpOptions.class).getProject());
+      projectPath = PubsubClient.projectPathFromId(projectId);
     }
 
     try {
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubWriteSchemaTransformProvider.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubWriteSchemaTransformProvider.java
index 2abd6f5fa95d..1626cf50b7c7 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubWriteSchemaTransformProvider.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/PubsubWriteSchemaTransformProvider.java
@@ -17,6 +17,8 @@
  */
 package org.apache.beam.sdk.io.gcp.pubsub;
 
+import static org.apache.beam.sdk.util.Preconditions.checkArgumentNotNull;
+
 import com.google.auto.service.AutoService;
 import java.io.Serializable;
 import java.nio.charset.StandardCharsets;
@@ -41,7 +43,6 @@
 import org.apache.beam.sdk.values.Row;
 import org.apache.beam.sdk.values.TupleTag;
 import org.apache.beam.sdk.values.TupleTagList;
-import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Strings;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.ImmutableSet;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Sets;
 
@@ -106,7 +107,10 @@ public void processElement(@Element Row row, MultiOutputReceiver receiver) throw
           for (int ix = 0; ix < fields.size(); ix++) {
             String name = fields.get(ix).getName();
             if (attributes != null && attributes.contains(name)) {
-              messageAttributes.put(name, row.getValue(ix));
+              String val = row.getString(ix);
+              if (val != null) {
+                messageAttributes.put(name, val);
+              }
             } else if (name.equals(attributesMap)) {
               Map<String, String> attrs = row.<String, String>getMap(ix);
               if (attrs != null) {
@@ -135,11 +139,11 @@ public void processElement(@Element Row row, MultiOutputReceiver receiver) throw
 
   @Override
   public SchemaTransform from(PubsubWriteSchemaTransformConfiguration configuration) {
-    if (!VALID_DATA_FORMATS.contains(configuration.getFormat().toUpperCase())) {
+    String format = checkArgumentNotNull(configuration.getFormat(), "Format must be specified");
+    if (!VALID_DATA_FORMATS.contains(format.toUpperCase())) {
       throw new IllegalArgumentException(
           String.format(
-              "Format %s not supported. Only supported formats are %s",
-              configuration.getFormat(), VALID_FORMATS_STR));
+              "Format %s not supported. Only supported formats are %s", format, VALID_FORMATS_STR));
     }
     return new PubsubWriteSchemaTransform(configuration);
   }
@@ -152,14 +156,10 @@ private static class PubsubWriteSchemaTransform extends SchemaTransform implemen
     }
 
     @Override
-    @SuppressWarnings({
-      "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-    })
     public PCollectionRowTuple expand(PCollectionRowTuple input) {
-      String errorOutput =
-          configuration.getErrorHandling() == null
-              ? null
-              : configuration.getErrorHandling().getOutput();
+      PubsubWriteSchemaTransformConfiguration.ErrorHandling errorHandling =
+          configuration.getErrorHandling();
+      String errorOutput = errorHandling == null ? null : errorHandling.getOutput();
 
       final Schema errorSchema =
           Schema.builder()
@@ -167,16 +167,19 @@ public PCollectionRowTuple expand(PCollectionRowTuple input) {
               .addNullableRowField("row", input.get("input").getSchema())
               .build();
 
-      String format = configuration.getFormat();
+      String format = checkArgumentNotNull(configuration.getFormat(), "Format must be specified");
       Schema beamSchema = input.get("input").getSchema();
       Schema payloadSchema;
-      if (configuration.getAttributes() == null && configuration.getAttributesMap() == null) {
+      List<String> attributes = configuration.getAttributes();
+      String attributesMap = configuration.getAttributesMap();
+      if (attributes == null && attributesMap == null) {
         payloadSchema = beamSchema;
       } else {
         Schema.Builder payloadSchemaBuilder = Schema.builder();
         for (Schema.Field f : beamSchema.getFields()) {
-          if (!configuration.getAttributes().contains(f.getName())
-              && !f.getName().equals(configuration.getAttributesMap())) {
+          boolean isAttribute = attributes != null && attributes.contains(f.getName());
+          boolean isAttributesMap = f.getName().equals(attributesMap);
+          if (!isAttribute && !isAttributesMap) {
             payloadSchemaBuilder.addField(f);
           }
         }
@@ -190,9 +193,12 @@ public PCollectionRowTuple expand(PCollectionRowTuple input) {
                   "Raw output only supported for single-field schemas, got %s", payloadSchema));
         }
         if (payloadSchema.getField(0).getType().equals(Schema.FieldType.BYTES)) {
-          fn = row -> row.getBytes(0);
+          fn = row -> checkArgumentNotNull(row.getBytes(0), "Payload bytes value cannot be null");
         } else if (payloadSchema.getField(0).getType().equals(Schema.FieldType.STRING)) {
-          fn = row -> row.getString(0).getBytes(StandardCharsets.UTF_8);
+          fn =
+              row ->
+                  checkArgumentNotNull(row.getString(0), "Payload string value cannot be null")
+                      .getBytes(StandardCharsets.UTF_8);
         } else {
           throw new IllegalArgumentException(
               String.format(
@@ -217,20 +223,23 @@ public PCollectionRowTuple expand(PCollectionRowTuple input) {
                   ParDo.of(
                           new ErrorFn(
                               fn,
-                              configuration.getAttributes(),
-                              configuration.getAttributesMap(),
+                              attributes,
+                              attributesMap,
                               payloadSchema,
                               errorSchema,
                               errorOutput != null))
                       .withOutputTags(OUTPUT_TAG, TupleTagList.of(ERROR_TAG)));
 
       PubsubIO.Write<PubsubMessage> writeTransform =
-          PubsubIO.writeMessages().to(configuration.getTopic());
-      if (!Strings.isNullOrEmpty(configuration.getIdAttribute())) {
-        writeTransform = writeTransform.withIdAttribute(configuration.getIdAttribute());
+          PubsubIO.writeMessages()
+              .to(checkArgumentNotNull(configuration.getTopic(), "Topic must be specified"));
+      String idAttribute = configuration.getIdAttribute();
+      if (idAttribute != null && !idAttribute.isEmpty()) {
+        writeTransform = writeTransform.withIdAttribute(idAttribute);
       }
-      if (!Strings.isNullOrEmpty(configuration.getTimestampAttribute())) {
-        writeTransform = writeTransform.withIdAttribute(configuration.getTimestampAttribute());
+      String timestampAttribute = configuration.getTimestampAttribute();
+      if (timestampAttribute != null && !timestampAttribute.isEmpty()) {
+        writeTransform = writeTransform.withTimestampAttribute(timestampAttribute);
       }
       outputTuple.get(OUTPUT_TAG).apply(writeTransform);
       outputTuple.get(ERROR_TAG).setRowSchema(errorSchema);
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsub.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsub.java
index a55de012d383..902c9ec44459 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsub.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsub.java
@@ -39,6 +39,7 @@
 import io.grpc.ManagedChannelBuilder;
 import java.io.IOException;
 import java.util.List;
+import java.util.Map;
 import java.util.concurrent.BlockingQueue;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.LinkedBlockingDeque;
@@ -71,9 +72,6 @@
  *
  * <p>Deletes topic and subscription on shutdown.
  */
-@SuppressWarnings({
-  "nullness" // TODO(https://github.com/apache/beam/issues/20497)
-})
 public class TestPubsub implements TestRule {
   private static final DateTimeFormatter DATETIME_FORMAT =
       DateTimeFormat.forPattern("YYYY-MM-dd-HH-mm-ss-SSS");
@@ -148,25 +146,29 @@ private void initializePubsub(Description description) throws IOException {
     } else {
       channel = ManagedChannelBuilder.forTarget(pubsubEndpoint).useTransportSecurity().build();
     }
-    channelProvider = FixedTransportChannelProvider.create(GrpcTransportChannel.create(channel));
-    topicAdmin =
+    TransportChannelProvider chanProvider =
+        FixedTransportChannelProvider.create(GrpcTransportChannel.create(channel));
+    channelProvider = chanProvider;
+    TopicAdminClient topAdmin =
         TopicAdminClient.create(
             TopicAdminSettings.newBuilder()
                 .setCredentialsProvider(pipelineOptions::getGcpCredential)
-                .setTransportChannelProvider(channelProvider)
+                .setTransportChannelProvider(chanProvider)
                 .setEndpoint(pubsubEndpoint)
                 .build());
-    subscriptionAdmin =
+    topicAdmin = topAdmin;
+    SubscriptionAdminClient subAdmin =
         SubscriptionAdminClient.create(
             SubscriptionAdminSettings.newBuilder()
                 .setCredentialsProvider(pipelineOptions::getGcpCredential)
-                .setTransportChannelProvider(channelProvider)
+                .setTransportChannelProvider(chanProvider)
                 .setEndpoint(pubsubEndpoint)
                 .build());
+    subscriptionAdmin = subAdmin;
     TopicPath eventsTopicPathTmp =
         PubsubClient.topicPathFromName(
             pipelineOptions.getProject(), createTopicName(description, EVENTS_TOPIC_NAME));
-    topicAdmin.createTopic(eventsTopicPathTmp.getPath());
+    topAdmin.createTopic(eventsTopicPathTmp.getPath());
 
     // Set this after successful creation; it signals that the topic needs teardown
     eventsTopicPath = eventsTopicPathTmp;
@@ -178,7 +180,7 @@ private void initializePubsub(Description description) throws IOException {
             String.format(
                 "projects/%s/subscriptions/%s", pipelineOptions.getProject(), subscriptionName));
 
-    subscriptionAdmin.createSubscription(
+    subAdmin.createSubscription(
         subscriptionPathTmp.getPath(),
         topicPath().getPath(),
         PushConfig.getDefaultInstance(),
@@ -188,25 +190,30 @@ private void initializePubsub(Description description) throws IOException {
   }
 
   private void tearDown() {
-    if (subscriptionAdmin == null || topicAdmin == null || channel == null) {
+    SubscriptionAdminClient subAdmin = subscriptionAdmin;
+    TopicAdminClient topAdmin = topicAdmin;
+    ManagedChannel chan = channel;
+    if (subAdmin == null || topAdmin == null || chan == null) {
       return;
     }
 
     try {
-      if (subscriptionPath != null) {
-        subscriptionAdmin.deleteSubscription(subscriptionPath.getPath());
+      SubscriptionPath subPath = subscriptionPath;
+      if (subPath != null) {
+        subAdmin.deleteSubscription(subPath.getPath());
       }
-      if (eventsTopicPath != null) {
+      TopicPath topPath = eventsTopicPath;
+      if (topPath != null) {
         for (String subscriptionPath :
-            topicAdmin.listTopicSubscriptions(eventsTopicPath.getPath()).iterateAll()) {
-          subscriptionAdmin.deleteSubscription(subscriptionPath);
+            topAdmin.listTopicSubscriptions(topPath.getPath()).iterateAll()) {
+          subAdmin.deleteSubscription(subscriptionPath);
         }
-        topicAdmin.deleteTopic(eventsTopicPath.getPath());
+        topAdmin.deleteTopic(topPath.getPath());
       }
     } finally {
-      subscriptionAdmin.close();
-      topicAdmin.close();
-      channel.shutdown();
+      subAdmin.close();
+      topAdmin.close();
+      chan.shutdown();
 
       subscriptionAdmin = null;
       topicAdmin = null;
@@ -251,31 +258,37 @@ static String createTopicName(Description description, String name) throws IOExc
 
   /** Topic path where events will be published to. */
   public TopicPath topicPath() {
-    return eventsTopicPath;
+    return Preconditions.checkNotNull(eventsTopicPath, "eventsTopicPath is not initialized");
   }
 
   /** Subscription path used to listen for messages on {@link #topicPath()}. */
   public SubscriptionPath subscriptionPath() {
-    return subscriptionPath;
+    return Preconditions.checkNotNull(subscriptionPath, "subscriptionPath is not initialized");
   }
 
   private List<String> listSubscriptions(TopicPath topicPath) {
-    Preconditions.checkNotNull(topicAdmin);
+    TopicAdminClient topAdmin =
+        Preconditions.checkNotNull(topicAdmin, "topicAdmin is not initialized");
+    SubscriptionPath subPath =
+        Preconditions.checkNotNull(subscriptionPath, "subscriptionPath is not initialized");
     // Exclude subscriptionPath, the subscription that we created
-    return Streams.stream(topicAdmin.listTopicSubscriptions(topicPath.getPath()).iterateAll())
-        .filter((path) -> !path.equals(subscriptionPath.getPath()))
+    return Streams.stream(topAdmin.listTopicSubscriptions(topicPath.getPath()).iterateAll())
+        .filter((path) -> !path.equals(subPath.getPath()))
         .collect(Collectors.toList());
   }
 
   /** Publish messages to {@link #topicPath()}. */
   public void publish(List<PubsubMessage> messages) {
-    Preconditions.checkNotNull(eventsTopicPath);
+    TopicPath topPath =
+        Preconditions.checkNotNull(eventsTopicPath, "eventsTopicPath is not initialized");
+    TransportChannelProvider chanProvider =
+        Preconditions.checkNotNull(channelProvider, "channelProvider is not initialized");
     Publisher eventPublisher;
     try {
       eventPublisher =
-          Publisher.newBuilder(eventsTopicPath.getPath())
+          Publisher.newBuilder(topPath.getPath())
               .setCredentialsProvider(pipelineOptions::getGcpCredential)
-              .setChannelProvider(channelProvider)
+              .setChannelProvider(chanProvider)
               .setEndpoint(pubsubEndpoint)
               .build();
     } catch (IOException e) {
@@ -288,8 +301,11 @@ public void publish(List<PubsubMessage> messages) {
                 (message) -> {
                   com.google.pubsub.v1.PubsubMessage.Builder builder =
                       com.google.pubsub.v1.PubsubMessage.newBuilder()
-                          .setData(ByteString.copyFrom(message.getPayload()))
-                          .putAllAttributes(message.getAttributeMap());
+                          .setData(ByteString.copyFrom(message.getPayload()));
+                  Map<String, String> attributeMap = message.getAttributeMap();
+                  if (attributeMap != null) {
+                    builder.putAllAttributes(attributeMap);
+                  }
                   return eventPublisher.publish(builder.build());
                 })
             .collect(Collectors.toList());
@@ -311,7 +327,10 @@ public void publish(List<PubsubMessage> messages) {
    */
   public List<PubsubMessage> waitForNMessages(int n, Duration timeoutDuration)
       throws IOException, InterruptedException {
-    Preconditions.checkNotNull(subscriptionPath);
+    SubscriptionPath subPath =
+        Preconditions.checkNotNull(subscriptionPath, "subscriptionPath is not initialized");
+    TransportChannelProvider chanProvider =
+        Preconditions.checkNotNull(channelProvider, "channelProvider is not initialized");
 
     BlockingQueue<com.google.pubsub.v1.PubsubMessage> receivedMessages =
         new LinkedBlockingDeque<>(n);
@@ -326,9 +345,9 @@ public List<PubsubMessage> waitForNMessages(int n, Duration timeoutDuration)
         };
 
     Subscriber subscriber =
-        Subscriber.newBuilder(subscriptionPath.getPath(), receiver)
+        Subscriber.newBuilder(subPath.getPath(), receiver)
             .setCredentialsProvider(pipelineOptions::getGcpCredential)
-            .setChannelProvider(channelProvider)
+            .setChannelProvider(chanProvider)
             .setEndpoint(pubsubEndpoint)
             .build();
     subscriber.startAsync();
@@ -369,10 +388,13 @@ public List<PubsubMessage> waitForNMessages(int n, Duration timeoutDuration)
    *     hasProperty("payload", equalTo("hello".getBytes(StandardCharsets.US_ASCII))),
    *     hasProperty("payload", equalTo("world".getBytes(StandardCharsets.US_ASCII))))
    *   .waitForUpTo(Duration.standardSeconds(20));
-   * </pre>
+   * }</pre>
    *
+   * @param matchers Matchers to assert on the received messages.
    */
-  public PollingAssertion assertThatTopicEventuallyReceives(Matcher<PubsubMessage>... matchers) {
+  @SafeVarargs
+  public final PollingAssertion assertThatTopicEventuallyReceives(
+      Matcher<PubsubMessage>... matchers) {
     return timeoutDuration ->
         assertThat(
             waitForNMessages(matchers.length, timeoutDuration), containsInAnyOrder(matchers));
diff --git a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsubSignal.java b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsubSignal.java
index f11ba9555a80..02b27886f233 100644
--- a/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsubSignal.java
+++ b/sdks/java/io/google-cloud-platform/src/main/java/org/apache/beam/sdk/io/gcp/pubsub/TestPubsubSignal.java
@@ -18,6 +18,7 @@
 package org.apache.beam.sdk.io.gcp.pubsub;
 
 import static org.apache.beam.sdk.io.gcp.pubsub.TestPubsub.createTopicName;
+import static org.apache.beam.sdk.util.Preconditions.checkStateNotNull;
 import static org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.base.Preconditions.checkState;
 
 import com.google.cloud.pubsub.v1.AckReplyConsumer;
@@ -74,7 +75,6 @@
  * <p>Uses a random temporary Pubsub topic for synchronization.
  */
 @SuppressWarnings({
-  "nullness", // TODO(https://github.com/apache/beam/issues/20497)
   // TODO(https://github.com/apache/beam/issues/21230): Remove when new version of
   // errorprone is released (2.11.0)
   "unused"
@@ -137,18 +137,20 @@ public void evaluate() throws Throwable {
   }
 
   private void initializePubsub(Description description) throws IOException {
-    topicAdmin =
+    TopicAdminClient topAdmin =
         TopicAdminClient.create(
             TopicAdminSettings.newBuilder()
                 .setCredentialsProvider(pipelineOptions::getGcpCredential)
                 .setEndpoint(pubsubEndpoint)
                 .build());
-    subscriptionAdmin =
+    topicAdmin = topAdmin;
+    SubscriptionAdminClient subAdmin =
         SubscriptionAdminClient.create(
             SubscriptionAdminSettings.newBuilder()
                 .setCredentialsProvider(pipelineOptions::getGcpCredential)
                 .setEndpoint(pubsubEndpoint)
                 .build());
+    subscriptionAdmin = subAdmin;
 
     // Example topic name:
     //    integ-test-TestClassName-testMethodName-2018-12-11-23-32-333-<random-long>-result
@@ -161,26 +163,26 @@ private void initializePubsub(Description description) throws IOException {
     SubscriptionPath resultSubscriptionPathTmp =
         PubsubClient.subscriptionPathFromName(
             pipelineOptions.getProject(),
-            "result-subscription-" + String.valueOf(ThreadLocalRandom.current().nextLong()));
+            "result-subscription-" + ThreadLocalRandom.current().nextLong());
     SubscriptionPath startSubscriptionPathTmp =
         PubsubClient.subscriptionPathFromName(
             pipelineOptions.getProject(),
-            "start-subscription-" + String.valueOf(ThreadLocalRandom.current().nextLong()));
+            "start-subscription-" + ThreadLocalRandom.current().nextLong());
 
     // Set variables after successful creation; this signals that they need teardown
-    topicAdmin.createTopic(resultTopicPathTmp.getPath());
+    topAdmin.createTopic(resultTopicPathTmp.getPath());
     resultTopicPath = resultTopicPathTmp;
-    topicAdmin.createTopic(startTopicPathTmp.getPath());
+    topAdmin.createTopic(startTopicPathTmp.getPath());
     startTopicPath = startTopicPathTmp;
-    subscriptionAdmin.createSubscription(
+    subAdmin.createSubscription(
         resultSubscriptionPathTmp.getPath(),
-        resultTopicPath.getPath(),
+        resultTopicPathTmp.getPath(),
         PushConfig.getDefaultInstance(),
         600);
     resultSubscriptionPath = resultSubscriptionPathTmp;
-    subscriptionAdmin.createSubscription(
+    subAdmin.createSubscription(
         startSubscriptionPathTmp.getPath(),
-        startTopicPath.getPath(),
+        startTopicPathTmp.getPath(),
         PushConfig.getDefaultInstance(),
         600);
     startSubscriptionPath = startSubscriptionPathTmp;
@@ -195,25 +197,31 @@ private static void logIfThrows(ThrowingRunnable runnable) {
   }
 
   private void tearDown() {
-    if (subscriptionAdmin == null || topicAdmin == null) {
+    SubscriptionAdminClient subAdmin = subscriptionAdmin;
+    TopicAdminClient topAdmin = topicAdmin;
+    if (subAdmin == null || topAdmin == null) {
       return;
     }
 
-    if (resultSubscriptionPath != null) {
-      logIfThrows(() -> subscriptionAdmin.deleteSubscription(resultSubscriptionPath.getPath()));
+    SubscriptionPath resSubPath = resultSubscriptionPath;
+    if (resSubPath != null) {
+      logIfThrows(() -> subAdmin.deleteSubscription(resSubPath.getPath()));
     }
-    if (startSubscriptionPath != null) {
-      logIfThrows(() -> subscriptionAdmin.deleteSubscription(startSubscriptionPath.getPath()));
+    SubscriptionPath startSubPath = startSubscriptionPath;
+    if (startSubPath != null) {
+      logIfThrows(() -> subAdmin.deleteSubscription(startSubPath.getPath()));
     }
-    if (resultTopicPath != null) {
-      logIfThrows(() -> topicAdmin.deleteTopic(resultTopicPath.getPath()));
+    TopicPath resTopPath = resultTopicPath;
+    if (resTopPath != null) {
+      logIfThrows(() -> topAdmin.deleteTopic(resTopPath.getPath()));
     }
-    if (startTopicPath != null) {
-      logIfThrows(() -> topicAdmin.deleteTopic(startTopicPath.getPath()));
+    TopicPath startTopPathVal = startTopicPath;
+    if (startTopPathVal != null) {
+      logIfThrows(() -> topAdmin.deleteTopic(startTopPathVal.getPath()));
     }
 
-    logIfThrows(subscriptionAdmin::close);
-    logIfThrows(topicAdmin::close);
+    logIfThrows(subAdmin::close);
+    logIfThrows(topAdmin::close);
 
     subscriptionAdmin = null;
     topicAdmin = null;
@@ -227,7 +235,7 @@ private void tearDown() {
 
   /** Outputs a message that the pipeline has started. */
   public PTransform<PBegin, PDone> signalStart() {
-    return new PublishStart(startTopicPath);
+    return new PublishStart(checkStateNotNull(startTopicPath, "startTopicPath is not initialized"));
   }
 
   /**
@@ -250,7 +258,11 @@ public <T> PTransform<PCollection<? extends T>, POutput> signalSuccessWhen(
       SerializableFunction<T, String> formatter,
       SerializableFunction<Set<T>, Boolean> successPredicate) {
 
-    return new PublishSuccessWhen<>(coder, formatter, successPredicate, resultTopicPath);
+    return new PublishSuccessWhen<>(
+        coder,
+        formatter,
+        successPredicate,
+        checkStateNotNull(resultTopicPath, "resultTopicPath is not initialized"));
   }
 
   /**
@@ -260,7 +272,7 @@ public <T> PTransform<PCollection<? extends T>, POutput> signalSuccessWhen(
   public <T> PTransform<PCollection<? extends T>, POutput> signalSuccessWhen(
       Coder<T> coder, SerializableFunction<Set<T>, Boolean> successPredicate) {
 
-    return signalSuccessWhen(coder, T::toString, successPredicate);
+    return signalSuccessWhen(coder, String::valueOf, successPredicate);
   }
 
   /**
@@ -270,10 +282,12 @@ public <T> PTransform<PCollection<? extends T>, POutput> signalSuccessWhen(
    * the start signal being published, which occurs immediately upon pipeline startup.
    */
   public Supplier<Void> waitForStart(Duration duration) {
+    SubscriptionPath subPath =
+        checkStateNotNull(startSubscriptionPath, "startSubscriptionPath is not initialized");
     return Suppliers.memoize(
         () -> {
           try {
-            String result = pollForResultForDuration(startSubscriptionPath, duration);
+            String result = pollForResultForDuration(subPath, duration);
             checkState(START_SIGNAL_MESSAGE.equals(result));
             return null;
           } catch (IOException e) {
@@ -284,7 +298,9 @@ public Supplier<Void> waitForStart(Duration duration) {
 
   /** Wait for a success signal for {@code duration}. */
   public void waitForSuccess(Duration duration) throws IOException {
-    String result = pollForResultForDuration(resultSubscriptionPath, duration);
+    SubscriptionPath subPath =
+        checkStateNotNull(resultSubscriptionPath, "resultSubscriptionPath is not initialized");
+    String result = pollForResultForDuration(subPath, duration);
     if (!RESULT_SUCCESS_MESSAGE.equals(result)) {
       throw new AssertionError(result);
     }
@@ -293,7 +309,7 @@ public void waitForSuccess(Duration duration) throws IOException {
   private String pollForResultForDuration(
       SubscriptionPath signalSubscriptionPath, Duration timeoutDuration) throws IOException {
 
-    AtomicReference<String> result = new AtomicReference<>(null);
+    AtomicReference<@Nullable String> result = new AtomicReference<>(null);
 
     MessageReceiver receiver =
         (com.google.pubsub.v1.PubsubMessage message, AckReplyConsumer replyConsumer) -> {
@@ -330,13 +346,14 @@ private String pollForResultForDuration(
     subscriber.stopAsync();
     subscriber.awaitTerminated();
 
-    if (result.get() == null) {
+    String resultVal = result.get();
+    if (resultVal == null) {
       throw new AssertionError(
           String.format(
               "Did not receive signal on %s in %ss",
               signalSubscriptionPath, timeoutDuration.getStandardSeconds()));
     }
-    return result.get();
+    return resultVal;
   }
 
   /** {@link PTransform} that signals once when the pipeline has started. */
@@ -397,7 +414,7 @@ public POutput expand(PCollection<? extends T> input) {
    * "FAILURE".
    */
   static class StatefulPredicateCheck<T> extends DoFn<KV<String, ? extends T>, String> {
-    private SerializableFunction<Set<T>, Boolean> successPredicate;
+    private final SerializableFunction<Set<T>, Boolean> successPredicate;
     // keep all events seen so far in the state cell
 
     private static final String SEEN_EVENTS = "seenEvents";