protected function sendRequest(Operation $operation, array $userValues = [], $async = false)
{
$operation->validate($userValues);
$options = (new RequestSerializer())->serializeOptions($operation, $userValues);
$method = $async ? 'requestAsync' : 'request';
$uri = uri_template($operation->getPath(), $userValues);
return $this->client->{$method}($operation->getMethod(), $uri, $options);
}