I have integrate exoplayer in my app, getting this error on clicking full-screen button

Question

FATAL EXCEPTION: main Process: com.flixo.videostreaming, PID: 5730 java.lang.IllegalStateException: Fragment HomeFragment{b5fddb4} (cb02f463-644e-4d0f-b742-696dba6c214d) not attached to an activity.

//all files uploaded github https://github.com/akash-softintra/player.git

please give me a solution.