puma 3.4.0 async response must have empty headers and body

[yellowsun]

Hi,
I'm developing an API system, ruby 2.2, rails 4.2.1 on Elastic Beanstalk. At first, I used Passenger as web server and websocket_rails gem at sync_fixes branch. Everything is perfect.
But now I want to switch to Puma, but I can't get the websocket connection on localhost. Whenever I call "http://localhost:3000/websocket" it throws "Puma caught this error: async response must have empty headers and body (RuntimeError)". I already tried to change to moaa/websocket_rails on threadsocket-rails branch but it still doesn't work, it throws 400 "Invalid"