code: public function encode()
      {
          $stream = '';
          foreach ($this->getAll() as $pair) {
              $stream .= '--' . $this->boundary . "\r\n";
              $stream .= $pair->asMime() . "\r\n";
          }
          $stream .= '--' . $this->boundary . "--\r\n";
  
          return $stream;
      }
docs: Renders the query string as a URL encoded request part.
  
  @return string        Part of URL.