/**
  * get oxSession object instance (create if needed)
  *
  * @return oxSession
  */
 public static function getInstance()
 {
     if (defined('OXID_PHP_UNIT')) {
         if (isset(modSession::$unitMOD) && is_object(modSession::$unitMOD)) {
             return modSession::$unitMOD;
         }
     }
     if (!isset(self::$_instance)) {
         self::$_instance = oxNew('oxsession');
     }
     return self::$_instance;
 }