public function getTransferDate($format = null)
    {
        $node = $this->getFirst('//epp:epp/epp:response/epp:resData/domain:infData/domain:trDate');
        if ($node === null) {
            return null;
        }

        if ($format === null) {
            return $node->nodeValue;
        }

        return date_create_from_format($format, $node->nodeValue);
    }