Exception on rotation of app

I/Choreographer: Skipped 54 frames!  The application may be doing too much work on its main thread.
I/OMXClient: MuxOMX ctor
D/EGL_emulation: eglMakeCurrent: 0xaf605340: ver 3 0 (tinfo 0xa3b278f0)
D/EGL_emulation: eglMakeCurrent: 0xaf605340: ver 3 0 (tinfo 0xa3b278f0)
D/EGL_emulation: eglMakeCurrent: 0xaf605340: ver 3 0 (tinfo 0xa3b278f0)
D/AudioTrack: Client defaulted notificationFrames to 6000 for frameCount 12000
D/MediaCodec: [OMX.google.h264.decoder] setting dataspace on output surface to #104
D/: HostConnection::get() New Host Connection established 0x93765500, tid 3942
D/SoftwareRenderer: setting dataspace on output surface to #104
D/AndroidRuntime: Shutting down VM


                  --------- beginning of crash
E/AndroidRuntime: FATAL EXCEPTION: main
                  Process: pl.nataliana.bakingapp, PID: 3727
                  java.lang.RuntimeException: Unable to pause activity {pl.nataliana.bakingapp/pl.nataliana.bakingapp.RecipeStepActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.exoplayer2.SimpleExoPlayer.setPlayWhenReady(boolean)' on a null object reference
                      at android.app.ActivityThread.performPauseActivityIfNeeded(ActivityThread.java:3751)
                      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3717)
                      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3691)
                      at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4489)
                      at android.app.ActivityThread.-wrap19(ActivityThread.java)
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1483)
                      at android.os.Handler.dispatchMessage(Handler.java:102)
                      at android.os.Looper.loop(Looper.java:154)
                      at android.app.ActivityThread.main(ActivityThread.java:6119)
                      at java.lang.reflect.Method.invoke(Native Method)
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
                   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void com.google.android.exoplayer2.SimpleExoPlayer.setPlayWhenReady(boolean)' on a null object reference
                      at pl.nataliana.bakingapp.fragment.RecipeStepFragment.onPause(RecipeStepFragment.java:134)
                      at android.support.v4.app.Fragment.performPause(Fragment.java:2531)
                      at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1485)
                      at android.support.v4.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManager.java:1759)
                      at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1827)
                      at android.support.v4.app.FragmentManagerImpl.dispatchStateChange(FragmentManager.java:3244)
                      at android.support.v4.app.FragmentManagerImpl.dispatchPause(FragmentManager.java:3216)
                      at android.support.v4.app.FragmentController.dispatchPause(FragmentController.java:228)
                      at android.support.v4.app.FragmentActivity.onPause(FragmentActivity.java:447)
                      at android.app.Activity.performPause(Activity.java:6819)
                      at android.app.Instrumentation.callActivityOnPause(Instrumentation.java:1322)
                      at android.app.ActivityThread.performPauseActivityIfNeeded(ActivityThread.java:3740)
                      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3717) 
                      at android.app.ActivityThread.performPauseActivity(ActivityThread.java:3691) 
                      at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4489) 
                      at android.app.ActivityThread.-wrap19(ActivityThread.java) 
                      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1483) 
                      at android.os.Handler.dispatchMessage(Handler.java:102) 
                      at android.os.Looper.loop(Looper.java:154) 
                      at android.app.ActivityThread.main(ActivityThread.java:6119) 
                      at java.lang.reflect.Method.invoke(Native Method) 
                      at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
                      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
Application terminated.