/**
  * @param array $params
  * @return string
  */
 public function mapDirectiveProductTypeByCategory($params = array())
 {
     // try to get value from parent first
     $value = $this->hasParentMap() ? $this->getParentMap()->mapDirectiveProductTypeByCategory($params) : '';
     if (empty($value)) {
         $value = parent::mapDirectiveProductTypeByCategory($params);
     }
     return $value;
 }