Multipart request problem

I'm trying to implement the request described [here](http://developers.strava.com/docs/reference/#api-Uploads-createUpload).

Using [this code](https://gist.github.com/gabornemeth/40ee3e2a8b0e20c9c8a7a6d7f47d415d) I receive error from the server complaining about "data_type" parameter is not supplied. I managed to post successful request with Postman.