This actually comes from `form-data`, request multipart manager. When you append a stream to the request, it needs to either have a .path attribute (as fs functions do) or a filename passed in options [1]. Because we don't pass any options [2] , the stream needs to have the .path attribute.

[2] https://github.com/mycozycloud/request-json/blob/master/main.coffee#L131
[1] https://github.com/felixge/node-form-data/blob/master/lib/form_data.js#L124-L127