private com.google.protobuf.SingleFieldBuilderV3<
            com.google.protobuf.FieldMask,
            com.google.protobuf.FieldMask.Builder,
            com.google.protobuf.FieldMaskOrBuilder>
        getUpdateMaskFieldBuilder() {
      if (updateMaskBuilder_ == null) {
        updateMaskBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.protobuf.FieldMask,
                com.google.protobuf.FieldMask.Builder,
                com.google.protobuf.FieldMaskOrBuilder>(
                getUpdateMask(), getParentForChildren(), isClean());
        updateMask_ = null;
      }
      return updateMaskBuilder_;
    }
<pre>
The list of fields to be updated. If empty, all fields are considered for
update.
</pre>

<code>.google.protobuf.FieldMask update_mask = 2;</code>
java-speech/proto-google-cloud-speech-v2/src/main/java/com/google/cloud/speech/v2/UpdateCustomClassRequest.java