public com.google.protobuf.FieldMask.Builder getUpdateMaskBuilder() {
      bitField0_ |= 0x00000002;
      onChanged();
      return getUpdateMaskFieldBuilder().getBuilder();
    }
<pre>
Required. Field mask is used to specify the fields to be overwritten in the
Index resource by the update. The fields specified in the update_mask are
relative to the resource, not the full request. A field of the resource
will be overwritten if it is in the mask. Empty field mask is not allowed.
If the mask is "*", it triggers a full update of the index, and also a
whole rebuild of index data.
</pre>

<code>.google.protobuf.FieldMask update_mask = 2 [(.google.api.field_behavior) = REQUIRED];
</code>
java-visionai/proto-google-cloud-visionai-v1/src/main/java/com/google/cloud/visionai/v1/UpdateIndexRequest.java