public Builder mergeGcsDataSink(
          com.google.storagetransfer.v1.proto.TransferTypes.GcsData value) {
        if (gcsDataSinkBuilder_ == null) {
          if (dataSinkCase_ == 4
              && dataSink_
                  != com.google.storagetransfer.v1.proto.TransferTypes.GcsData
                      .getDefaultInstance()) {
            dataSink_ =
                com.google.storagetransfer.v1.proto.TransferTypes.GcsData.newBuilder(
                        (com.google.storagetransfer.v1.proto.TransferTypes.GcsData) dataSink_)
                    .mergeFrom(value)
                    .buildPartial();
          } else {
            dataSink_ = value;
          }
          onChanged();
        } else {
          if (dataSinkCase_ == 4) {
            gcsDataSinkBuilder_.mergeFrom(value);
          } else {
            gcsDataSinkBuilder_.setMessage(value);
          }
        }
        dataSinkCase_ = 4;
        return this;
      }
<pre>
A Cloud Storage data sink.
</pre>

<code>.google.storagetransfer.v1.GcsData gcs_data_sink = 4;</code>
java-storage-transfer/proto-google-cloud-storage-transfer-v1/src/main/java/com/google/storagetransfer/v1/proto/TransferTypes.java