code: public function toNode(DOMDocument $document = null)
      {
          if (null === $document) {
              $document = new DOMDocument();
          }
  
          $node = $document->createElement('QueryRequest');
  
          if ($this->getShipment() !== null) {
              $node->appendChild($this->getShipment()->toNode($document));
          }
          $node->appendChild(
              $document->createElement(
                  'SuppressQuestionIndicator',
                  ($this->isSuppressQuestionIndicator() ? 'Y' : 'N')
              )
          );
  
          return $node;
      }
docs: @param null|DOMDocument $document
  
  @return DOMElement