protected function _assignPersistentParam()
    {
        // Persistent Parameter Handling
        $aPersParam = \OxidEsales\Eshop\Core\Registry::getSession()->getVariable('persparam');
        if (isset($aPersParam) && isset($aPersParam[$this->getId()])) {
            $this->_aPersistParam = $aPersParam[$this->getId()];
        }
    }