public function getExpiryDate($format = null)
    {
        $expiryDate = $this->getDataItem('ExpiryDate');

        if ($format === null || $expiryDate === null) {
            return $expiryDate;
        } else {
            return gmdate(
                $format,
                gmmktime(0, 0, 0, $this->getExpiryMonth(), 1, $this->getExpiryYear())
            );
        }
    }