private com.google.protobuf.SingleFieldBuilderV3<
              com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystem,
              com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystem.Builder,
              com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystemOrBuilder>
          getPosixDataSinkFieldBuilder() {
        if (posixDataSinkBuilder_ == null) {
          if (!(dataSinkCase_ == 13)) {
            dataSink_ =
                com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystem
                    .getDefaultInstance();
          }
          posixDataSinkBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystem,
                  com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystem.Builder,
                  com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystemOrBuilder>(
                  (com.google.storagetransfer.v1.proto.TransferTypes.PosixFilesystem) dataSink_,
                  getParentForChildren(),
                  isClean());
          dataSink_ = null;
        }
        dataSinkCase_ = 13;
        onChanged();
        return posixDataSinkBuilder_;
      }
<pre>
A POSIX Filesystem data sink.
</pre>

<code>.google.storagetransfer.v1.PosixFilesystem posix_data_sink = 13;</code>
java-storage-transfer/proto-google-cloud-storage-transfer-v1/src/main/java/com/google/storagetransfer/v1/proto/TransferTypes.java