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>
Field mask is used to specify the fields to be overwritten in the Input
resource by the update. You can only update the following fields:

* [`tier`](https://cloud.google.com/livestream/docs/reference/rest/v1/projects.locations.inputs#Tier)
* [`preprocessingConfig`](https://cloud.google.com/livestream/docs/reference/rest/v1/projects.locations.inputs#PreprocessingConfig)
* [`securityRules`](https://cloud.google.com/livestream/docs/reference/rest/v1/projects.locations.inputs#SecurityRule)

The fields specified in the update_mask are relative to the resource, not
the full request. A field will be overwritten if it is in the mask.

If the mask is not present, then each field from the list above is updated
if the field appears in the request payload. To unset a field, add the
field to the update mask and remove it from the request payload.
</pre>

<code>.google.protobuf.FieldMask update_mask = 1;</code>
java-video-live-stream/proto-google-cloud-live-stream-v1/src/main/java/com/google/cloud/video/livestream/v1/UpdateInputRequest.java