public function has_data($idx=null)
	{
    if ( !\is_array($this->data) ){
      return false;
    }
    if ( \is_null($idx) ){
      return !empty($this->data);
    }
    $args = \func_get_args();
    foreach ( $args as $arg ){
      if ( !isset($this->data[$idx]) ){
        return false;
      }
    }
    return true;
	}