public function update($code = '')
 {
     $param = $this->getParameters();
     if ($param && count($param) === 1 && array_key_exists('billing_info', $param) && array_key_exists('credit_card', $param['billing_info'])) {
         if (!empty($code)) {
             $this->setCode($code);
         }
         return $this->client->put($this->getBaseUrl() . $this->getCode() . '/billing_infos', $param['billing_info']);
     }
     return parent::update($code);
 }