Unexpected end of input on ember .save(), empty responseText

I'm doing a PUT request with ember .save() method. Returned status is 200, but I keep getting the "unexpected end of input error". I think it might be because request is returning and empty json responseText as shown here :

http://ift.tt/1djVkjk

Do you have any ideas how I can solve this problem or the exact reason I get this error?