public function serializeAttribute($name)
    {
        if ($name === 'issuanceCloseDate') {
            $val = $this->getIssuanceCloseDate();
            if ($val instanceof \DateTimeInterface) {
                $val = $val->format(\DateTime::RFC3339);
            }
            return (string)$val;
        }
        return parent::serializeAttribute($name);
    }