@java.lang.Override
  public Builder toBuilder() {
    return this == DEFAULT_INSTANCE ? new Builder() : new Builder().mergeFrom(this);
  }
<pre>
The list of fields to be updated.
- Unset `update_mask` or set `update_mask` to be a single "*" only will
  update all updatable fields with the value provided in `collection`.
- To update `display_name` value to empty string, set it in the
`collection`
  to empty string, and set `update_mask` with "display_name". Same applies
  to other updatable string fields in the `collection`.
</pre>

<code>.google.protobuf.FieldMask update_mask = 2;</code>
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/UpdateCollectionRequest.java