code: @InternalApi
    public PartialUpdateInstanceRequest toProto(String projectId) {
      // Empty field mask implies full resource replacement, which would clear all fields in an empty
      // update request.
      Preconditions.checkState(
          !builder.getUpdateMask().getPathsList().isEmpty(), "Update request is empty");
  
      builder.getInstanceBuilder().setName(NameUtil.formatInstanceName(projectId, instanceId));
  
      return builder.build();
    }
docs: Creates the request protobuf. This method is considered an internal implementation detail and
  not meant to be used by applications.