refactor: add null annotations in appropriate places

Add @nullable annotations and move existing ones to appropriate places. It was influenced by Recommentations for making ADK Java more idiomatic, but it was later reevaluated to use different approach towards wrapper vs primitive types and mostly stay with existing solution. The changes are supposed to make the code more consistent in places where @nullable is either used or unused.

PiperOrigin-RevId: 890340769

Author: MiloszSobczyk

core/src/main/java/com/google/adk/agents/ActiveStreamingTool.java

@@ -22,8 +22,8 @@
 
 /** Manages streaming tool related resources during invocation. */
 public class ActiveStreamingTool {
-  @Nullable private Disposable task;
-  @Nullable private LiveRequestQueue stream;
+  private @Nullable Disposable task;
+  private @Nullable LiveRequestQueue stream;
 
   public ActiveStreamingTool(Disposable task) {
     this(task, null);
@@ -41,8 +41,7 @@ public ActiveStreamingTool(Disposable task, LiveRequestQueue stream) {
   public ActiveStreamingTool() {}
 
   /** Returns the active task of this streaming tool. */
-  @Nullable
-  public Disposable task() {
+  public @Nullable Disposable task() {
     return task;
   }
 
@@ -52,8 +51,7 @@ public void task(@Nullable Disposable task) {
   }
 
   /** Returns the active stream of this streaming tool. */
-  @Nullable
-  public LiveRequestQueue stream() {
+  public @Nullable LiveRequestQueue stream() {
     return stream;
   }
 

core/src/main/java/com/google/adk/agents/LlmAgent.java

@@ -129,10 +129,10 @@ protected LlmAgent(Builder builder) {
         requireNonNullElse(builder.globalInstruction, new Instruction.Static(""));
     this.generateContentConfig = Optional.ofNullable(builder.generateContentConfig);
     this.includeContents = requireNonNullElse(builder.includeContents, IncludeContents.DEFAULT);
-    this.planning = builder.planning != null && builder.planning;
+    this.planning = requireNonNullElse(builder.planning, false);
     this.maxSteps = Optional.ofNullable(builder.maxSteps);
-    this.disallowTransferToParent = builder.disallowTransferToParent;
-    this.disallowTransferToPeers = builder.disallowTransferToPeers;
+    this.disallowTransferToParent = requireNonNullElse(builder.disallowTransferToParent, false);
+    this.disallowTransferToPeers = requireNonNullElse(builder.disallowTransferToPeers, false);
     this.beforeModelCallback = requireNonNullElse(builder.beforeModelCallback, ImmutableList.of());
     this.afterModelCallback = requireNonNullElse(builder.afterModelCallback, ImmutableList.of());
     this.onModelErrorCallback =
@@ -566,8 +566,7 @@ public Builder codeExecutor(BaseCodeExecutor codeExecutor) {
       return this;
     }
 
-    @Nullable
-    private static <B, A> ImmutableList<A> convertCallbacks(
+    private static <B, A> @Nullable ImmutableList<A> convertCallbacks(
         @Nullable List<? extends B> callbacks, Function<B, A> converter, String callbackType) {
       return Optional.ofNullable(callbacks)
           .map(

core/src/main/java/com/google/adk/apps/App.java

@@ -40,8 +40,8 @@ public class App {
   private final String name;
   private final BaseAgent rootAgent;
   private final ImmutableList<? extends Plugin> plugins;
-  @Nullable private final EventsCompactionConfig eventsCompactionConfig;
-  @Nullable private final ContextCacheConfig contextCacheConfig;
+  private final @Nullable EventsCompactionConfig eventsCompactionConfig;
+  private final @Nullable ContextCacheConfig contextCacheConfig;
 
   private App(
       String name,

core/src/main/java/com/google/adk/events/Event.java

@@ -348,7 +348,7 @@ public static class Builder {
     private String invocationId;
     private String author;
     private @Nullable Content content;
-    private EventActions actions;
+    private @Nullable EventActions actions;
     private @Nullable Set<String> longRunningToolIds;
     private @Nullable Boolean partial;
     private @Nullable Boolean turnComplete;
@@ -399,7 +399,7 @@ public Builder content(@Nullable Content value) {
 
     @CanIgnoreReturnValue
     @JsonProperty("actions")
-    public Builder actions(EventActions value) {
+    public Builder actions(@Nullable EventActions value) {
       this.actions = value;
       return this;
     }

core/src/main/java/com/google/adk/events/EventActions.java

@@ -281,7 +281,7 @@ private Builder(EventActions eventActions) {
 
     @CanIgnoreReturnValue
     @JsonProperty("skipSummarization")
-    public Builder skipSummarization(boolean skipSummarization) {
+    public Builder skipSummarization(@Nullable Boolean skipSummarization) {
       this.skipSummarization = skipSummarization;
       return this;
     }
@@ -324,7 +324,7 @@ public Builder transferToAgent(@Nullable String agentId) {
 
     @CanIgnoreReturnValue
     @JsonProperty("escalate")
-    public Builder escalate(boolean escalate) {
+    public Builder escalate(@Nullable Boolean escalate) {
       this.escalate = escalate;
       return this;
     }