Fix addExperiment() to handle immutable lists and remove redundant defensive copies

Author: ash6898

runners/google-cloud-dataflow-java/src/main/java/org/apache/beam/runners/dataflow/DataflowPipelineTranslator.java

@@ -403,10 +403,6 @@ public Translator(Pipeline pipeline, DataflowRunner runner, SdkComponents sdkCom
      * @return a Job definition filled in with the type of job, the environment, and the job steps.
      */
     public Job translate(List<DataflowPackage> packages) {
-      // Ensure the experiments list is mutable before any experiments are added.
-      if (options.getExperiments() != null) {
-        options.setExperiments(new ArrayList<>(options.getExperiments()));
-      }
       job.setName(options.getJobName().toLowerCase());
 
       Environment environment = new Environment();

runners/google-cloud-dataflow-java/src/main/java/org/apache/beam/runners/dataflow/DataflowRunner.java

@@ -1243,10 +1243,6 @@ private static boolean includesTransformUpgrades(Pipeline pipeline) {
   @SuppressWarnings("Slf4jFormatShouldBeConst")
   @Override
   public DataflowPipelineJob run(Pipeline pipeline) {
-    // Ensure the experiments list is mutable before any experiments are added.
-    if (options.getExperiments() != null) {
-      options.setExperiments(new ArrayList<>(options.getExperiments()));
-    }
     // Multi-language pipelines and pipelines that include upgrades should automatically be upgraded
     // to Dataflow Portable Runner.
     if (DataflowRunner.isMultiLanguagePipeline(pipeline) || includesTransformUpgrades(pipeline)) {

runners/google-cloud-dataflow-java/worker/src/main/java/org/apache/beam/runners/dataflow/worker/windmill/client/grpc/GrpcWindmillServer.java

@@ -111,10 +111,6 @@ private static DataflowWorkerHarnessOptions testOptions(
       boolean enableStreamingEngine, List<String> additionalExperiments) {
     DataflowWorkerHarnessOptions options =
         PipelineOptionsFactory.create().as(DataflowWorkerHarnessOptions.class);
-    // Ensure the experiments list is mutable before any experiments are added.
-    if (options.getExperiments() != null) {
-      options.setExperiments(new ArrayList<>(options.getExperiments()));
-    }
     options.setProject("project");
     options.setJobId("job");
     options.setWorkerId("worker");

sdks/java/core/src/main/java/org/apache/beam/sdk/options/ExperimentalOptions.java

@@ -17,6 +17,7 @@
  */
 package org.apache.beam.sdk.options;
 
+import java.util.ArrayList;
 import java.util.List;
 import org.apache.beam.vendor.guava.v32_1_2_jre.com.google.common.collect.Lists;
 import org.checkerframework.checker.nullness.qual.Nullable;
@@ -57,9 +58,7 @@ static boolean hasExperiment(PipelineOptions options, String experiment) {
   /** Adds experiment to options if not already present. */
   static void addExperiment(ExperimentalOptions options, String experiment) {
     List<String> experiments = options.getExperiments();
-    if (experiments == null) {
-      experiments = Lists.newArrayList();
-    }
+    experiments = (experiments == null) ? Lists.newArrayList() : new ArrayList<>(experiments);
     if (!experiments.contains(experiment)) {
       experiments.add(experiment);
     }