code: public function toNode(DOMDocument $document = null)
      {
          if (null === $document) {
              $document = new DOMDocument();
          }
  
          $node = $document->createElement('Product');
          for ($i = 1; $i <= 3; $i++) {
              $desc = $this->{'getDescription'.$i}();
              if ($desc !== null) {
                  $node->appendChild($document->createElement('Description', $desc));
              }
          }
          if ($this->getUnit() !== null) {
              $node->appendChild($this->getUnit()->toNode($document));
          }
          if ($this->getCommodityCode() !== null) {
              $node->appendChild($document->createElement('CommodityCode', $this->getCommodityCode()));
          }
          if ($this->getPartNumber() !== null) {
              $node->appendChild($document->createElement('PartNumber', $this->getPartNumber()));
          }
          if ($this->getOriginCountryCode() !== null) {
              $node->appendChild($document->createElement('OriginCountryCode', $this->getOriginCountryCode()));
          }
  
          return $node;
      }
docs: @param null|DOMDocument $document
  
  @return DOMElement