public function clear($sKey)
    {
        if (empty($sKey)) {
            return;
        }

        $this->clearDefaultStorageValue($sKey);

        //Get auth user object
        $obUser = UserHelper::instance()->getUser();
        if (empty($obUser)) {
            return;
        }

        $obUser->$sKey = null;
        $obUser->save();
    }