public function getItem($itemType, $id, array $queryString = []) {
      $options = [];
      if ($queryString) {
         $options['query'] = $queryString;
      }
      $response = $this->client->request('get', $itemType . '/' . $id, $options);
      return [
         'statusCode' => $response->getStatusCode(),
         'body' => $response->getBody()->getContents(),
      ];
   }