public function toXML(DOMElement $parent = null) : DOMElement
    {
        if ($parent === null) {
            $parent = DOMDocumentFactory::create();
            $doc = $parent;
        } else {
            $doc = $parent->ownerDocument;
        }
        $element = $doc->createElementNS(Constants::NS_SAML, $this->nodeName);
        $parent->appendChild($element);

        if ($this->NameQualifier !== null) {
            $element->setAttribute('NameQualifier', $this->NameQualifier);
        }

        if ($this->SPNameQualifier !== null) {
            $element->setAttribute('SPNameQualifier', $this->SPNameQualifier);
        }

        return $element;
    }