Inheritance: extends AbstractQuerySecurity
 /**
  * @param $maxDepth
  *
  * @return QueryComplexity
  */
 protected function getRule($maxDepth = null)
 {
     if (null === self::$rule) {
         self::$rule = new QueryComplexity($maxDepth);
     } elseif (null !== $maxDepth) {
         self::$rule->setMaxQueryComplexity($maxDepth);
     }
     return self::$rule;
 }