Google Tasks PHP add multipart file

Question

I'm using the Google Tasks PHP SDK. It works very when I send a basic url with parameters. But I don't know how can I do to add multipart files to request.

Here is my function to build a request :

private function newTaskRequest($method, $url, $headers, $body)
{
    $httpRequest = new HttpRequest();
    $httpRequest->setHttpMethod($method);
    $httpRequest->setUrl($url);
    $httpRequest->setHeaders($headers);
    $httpRequest->setBody($body);

    $task = new Task();
    $task->setHttpRequest($httpRequest);

    return $task;
}

And this is how I use it :

$data = json_encode([
     'param1'  => 'hey',
     'param2'  => 'yoo',
]);

$task = $this->newTaskRequest(HttpMethod::POST, $url, $headers, $data);
$response = $this->client->createTask($this->queueName, $task);

I didn't find any method to add a file to my request. It is possible to send a file to google tasks ?