public Builder mergeGcsSource(com.google.cloud.translate.v3.GcsInputSource value) {
        if (gcsSourceBuilder_ == null) {
          if (sourceCase_ == 3
              && source_ != com.google.cloud.translate.v3.GcsInputSource.getDefaultInstance()) {
            source_ =
                com.google.cloud.translate.v3.GcsInputSource.newBuilder(
                        (com.google.cloud.translate.v3.GcsInputSource) source_)
                    .mergeFrom(value)
                    .buildPartial();
          } else {
            source_ = value;
          }
          onChanged();
        } else {
          if (sourceCase_ == 3) {
            gcsSourceBuilder_.mergeFrom(value);
          } else {
            gcsSourceBuilder_.setMessage(value);
          }
        }
        sourceCase_ = 3;
        return this;
      }
<pre>
Google Cloud Storage file source.
</pre>

<code>.google.cloud.translation.v3.GcsInputSource gcs_source = 3;</code>
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/DatasetInputConfig.java