code: private function secondParamValidation(Event $event)
      {
          $params = $event->getCustomParams();
          return (!isset($params[1]) || (is_numeric($params[1]) && $params[1] >= 1 && $params[1] <= $this->maxDieSides));
      }
docs: Verify parameter 2 is valid
  
  @param Event $event
  @return bool