protected function get_meta_data($instance)
 {
     $data = parent::get_meta_data($instance);
     if (empty($data->roles) || !is_array($data->roles)) {
         $data->roles = array(self::ADMINISTRATOR_ROLE_KEY);
     }
     if (!in_array(self::ADMINISTRATOR_ROLE_KEY, $data->roles)) {
         array_unshift($data->roles, self::ADMINISTRATOR_ROLE_KEY);
     }
     return $data;
 }