Cannot upload file in Rest Context when using BrowserKit

[brunoroux]

Using this scenario :

Scenario: Check that I can upload a new media
        When I send a "POST" request to "/sites/14/uploads/media" with parameters:
            | key                                           | value        |
            | api_upload_media[medias][0] | @box.png |
        Then the response status code should be 201
        And the JSON node with path "0.id" should be equal to "99"

I get the following error :
An uploaded file must be an array or an instance of UploadedFile. (InvalidArgumentException)