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I have a crash on tablet that is quite misterious to me :

java.lang.NullPointerException: Attempt to read from field 'int android.support.v4.app.Fragment.mContainerId' on a null object reference                                                                          
   at android.support.v4.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1012)                                                                          
   at android.support.v4.app.FragmentTransition.calculateFragments(FragmentTransition.java:971)                                                                          
   at android.support.v4.app.FragmentTransition.startTransitions(FragmentTransition.java:95)                                                                          
   at android.support.v4.app.FragmentManagerImpl.executeOpsTogether(FragmentManager.java:2143)                                                                          
   at android.support.v4.app.FragmentManagerImpl.optimizeAndExecuteOps(FragmentManager.java:2098)                                                                          
   at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:2008)                                                                          
   at android.support.v4.app.FragmentManagerImpl$1.run(FragmentManager.java:710)                                                                          
   at android.os.Handler.handleCallback(Handler.java:751)                                                                          
   at android.os.Handler.dispatchMessage(Handler.java:95)                                                                          
   at android.os.Looper.loop(Looper.java:154)                                                                          
   at android.app.ActivityThread.main(ActivityThread.java:6077)                                                                          
   at java.lang.reflect.Method.invoke(Native Method)                                                                          
   at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:865)                                                                          
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:755)
It only happens on my api 24 Pixel C. Debug mode couldn't help me to find out where. It happends when I clic a button that removes a fragment, but the "fragment removing" part of code gets executed correctly, something happends after execution of my OnClickListener. 
I removed transaction animations and got the same crash.
Has anybody experienced that before ?
Thanks
                @RoShanShan It was indeed the way that I did remove the fragment, I updated my original post with the solution
– Renaud Favier
                Feb 23, 2017 at 16:01
Seems that the solution were not to keep a reference of the fragment but find it with tag : 
Before : 
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
courseLauncherFragment = CourseLauncherFragment.newInstance(courseId);
fragmentTransaction.replace(R.id.launcher_finish_frame_layout, courseLauncherFragment);
fragmentTransaction.commit();
getSupportFragmentManager().executePendingTransactions();
then to remove it : 
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.slide_in_left, R.anim.slide_out_left);
fragmentTransaction.remove(courseLauncherFragment);
fragmentTransaction.commit();
And now : 
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.launcher_finish_frame_layout, CourseLauncherFragment.newInstance(courseId), LAUNCHER_FRAGMENT_TAG);
fragmentTransaction.commit();
getSupportFragmentManager().executePendingTransactions();
then : 
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.slide_in_left, R.anim.slide_out_left);
Fragment fragment = fragmentManager.findFragmentByTag(LAUNCHER_FRAGMENT_TAG);
fragmentTransaction.remove(fragment);
fragmentTransaction.commit();
        
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