code: protected function contributorDefined()
      {
          if (null === $this->username && !$this->configurationHandler->isTheme()) {
              $exception = array(
                  "message" => 'exception_contributor_not_defined',
                  "show_exception" => true,
              );
              throw new LogicException(json_encode($exception));
          }
      }
docs: Checks the page contributor has been set