public Builder mergeGcsSource(com.google.cloud.translate.v3.GcsSource value) {
      if (gcsSourceBuilder_ == null) {
        if (sourceCase_ == 2
            && source_ != com.google.cloud.translate.v3.GcsSource.getDefaultInstance()) {
          source_ =
              com.google.cloud.translate.v3.GcsSource.newBuilder(
                      (com.google.cloud.translate.v3.GcsSource) source_)
                  .mergeFrom(value)
                  .buildPartial();
        } else {
          source_ = value;
        }
        onChanged();
      } else {
        if (sourceCase_ == 2) {
          gcsSourceBuilder_.mergeFrom(value);
        } else {
          gcsSourceBuilder_.setMessage(value);
        }
      }
      sourceCase_ = 2;
      return this;
    }
<pre>
Google Cloud Storage location. This must be a single file.
For example: gs://example_bucket/example_file.pdf
</pre>

<code>.google.cloud.translation.v3.GcsSource gcs_source = 2;</code>
java-translate/proto-google-cloud-translate-v3/src/main/java/com/google/cloud/translate/v3/DocumentInputConfig.java