public function getMustFillFields()
    {
        if ($this->_aMustFillFields === null) {
            $this->_aMustFillFields = false;

            // passing must-be-filled-fields info
            $mustFillFields = \OxidEsales\Eshop\Core\Registry::getConfig()->getConfigParam('aMustFillFields');
            if (is_array($mustFillFields)) {
                $this->_aMustFillFields = array_flip($mustFillFields);
            }
        }

        return $this->_aMustFillFields;
    }