add nullable annotation

Author: itsankit-google

src/main/java/io/cdap/plugin/gcp/bigquery/sqlengine/BigQuerySQLEngine.java

@@ -160,7 +160,7 @@ public void prepareRun(SQLEngineContext context) throws Exception {
     storage = GCPUtils.getStorage(project, credentials);
     Dataset dataset = bigQuery.getDataset(DatasetId.of(datasetProject, datasetName));
     bucket = BigQueryUtil.getStagingBucketName(context.getRuntimeArguments(), sqlEngineConfig.getLocation(),
-                                               dataset, null);
+                                               dataset, sqlEngineConfig.getBucket());
 
     String cmekKey = !Strings.isNullOrEmpty(sqlEngineConfig.cmekKey) ? sqlEngineConfig.cmekKey :
       ctx.getRuntimeArguments().get(CmekUtils.CMEK_KEY);
@@ -175,7 +175,8 @@ public void prepareRun(SQLEngineContext context) throws Exception {
                                       sqlEngineConfig.getLocation(), cmekKeyName);
     // Configure GCS bucket that is used to stage temporary files.
     // If the bucket is created for this run, mark it for deletion after executon is completed
-    BigQuerySinkUtils.configureBucket(configuration, bucket, "bqpushdown-" + runId);
+    String fallbackBucketName = "bqpushdown-" + runId;
+    BigQuerySinkUtils.configureBucket(configuration, bucket, fallbackBucketName);
 
     // Configure credentials for the source
     BigQuerySourceUtils.configureServiceAccount(configuration, sqlEngineConfig.connection);

src/main/java/io/cdap/plugin/gcp/bigquery/util/BigQueryUtil.java

@@ -868,6 +868,7 @@ public static Map<String, String> getJobTags(String jobType) {
    * @param bucket bucket from plugin configuration
    * @return Bucket name to use for this sink.
    */
+  @Nullable
   public static String getStagingBucketName(Map<String, String> arguments, @Nullable String configLocation,
                                             @Nullable Dataset dataset, @Nullable String bucket) {
     // Get Bucket Prefix from configuration

src/main/java/io/cdap/plugin/gcp/dataplex/sink/DataplexBatchSink.java

@@ -293,7 +293,8 @@ private void prepareRunBigQueryDataset(BatchSinkContext context) throws Exceptio
     Dataset dataset = bigQuery.getDataset(datasetId);
     String bucket = BigQueryUtil.getStagingBucketName(context.getArguments().asMap(), config.getLocation(),
                                                       dataset, null);
-    bucket = BigQuerySinkUtils.configureBucket(baseConfiguration, bucket, "dataplex-" + runUUID);
+    String fallbackBucketName = "dataplex-" + runUUID;
+    bucket = BigQuerySinkUtils.configureBucket(baseConfiguration, bucket, fallbackBucketName);
     if (!context.isPreviewEnabled()) {
       BigQuerySinkUtils.createResources(bigQuery, GCPUtils.getStorage(project, credentials),
         DatasetId.of(datasetProject, datasetName),