code: @Override
      public final RESTResponse invoke() {
          UNode outNode = invokeUNodeOut();
          assert outNode != null;
          return new RESTResponse(HttpCode.OK,
                                  outNode.toString(m_request.getOutputContentType()),
                                  m_request.getOutputContentType());
      }
docs: Declared "final" so subclass does not attempt to override.