Changing deprecated Logger.warn to Logger.warning
Fix _json_request to correctly catch json decode error - as of requests 1.0 (https://github.com/kennethreitz/requests/commit/1451ba0c6d395c41f86da35036fa361c3a41bc90#diff-afd5aad80649cdfae687bee05242c8faL531), response.json raises an exception instead of returning None when there's no JSON.