code: public function toNode(DOMDocument $document = null)
      {
          if (null === $document) {
              $document = new DOMDocument();
          }
  
          $node = $document->createElement('Shipper');
  
          $shipperName = $this->getName();
          if (isset($shipperName)) {
              $node->appendChild($document->createElement('Name', $shipperName));
          }
  
          $shipperNumber = $this->getShipperNumber();
          if (isset($shipperNumber)) {
              $node->appendChild($document->createElement('ShipperNumber', $shipperNumber));
          }
  
          $address = $this->getAddress();
          if (isset($address)) {
              $node->appendChild($address->toNode($document));
          }
  
          return $node;
      }
docs: @param null|DOMDocument $document
  
  @return DOMElement