code: protected function loadMappingFile($file)
      {
          $xmlElement = simplexml_load_file($file);
          $types = array('mapped-superclass', 'entity', 'document');
  
          foreach ($types as $type) {
              if (isset($xmlElement->$type)) {
                  $className = $this->getAttribute($xmlElement->$type, 'name');
  
                  return array($className => $xmlElement->$type);
              }
          }
  
          return null;
      }
docs: {@inheritDoc}