Python requests, PUT empty data

I am trying to use request to PUT some data as such,

r = requests.put(
        url,
        data={'tiles': []},
        headers={'x-auth-token': token}
    )

However, tiles is not sent if it is just an empty list. tiles only appears when the data is not empty. I checked this with http://httpbin.org/put also.

Does anyone have any ideas how to put empty data?