Crash - calling onFragmentCreated after onDestory() was called on parent

Question

I got some crash trace from Crashlytics service and I need some help to understand what cause them.

I use the next flow :

I have my main GeneralActivity and inside that Activity I lunch a fragment that uses MyMainFragment and he uses ViewPager to display pages, each page is called MyPage and he extend BaseFragment . Basically what I getting is a fragment with some pages to scroll using the FragmentStatePagerAdapter.

Sometimes I see users get crash because the main Activity BaseActivity calls onDestroy(). My question is why after calling onDestory it never get into the the dispose() in MyPage method but it enters into onFragmentCreated.

Fatal Exception: java.lang.RuntimeException: Unable to destroy activity {com.myApp.GeneralActivity}: java.lang.NullPointerException
       at android.app.ActivityThread.performDestroyActivity(ActivityThread.java:3565)
       at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:3584)
       at android.app.ActivityThread.access$1300(ActivityThread.java:157)
       at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1342)
       at android.os.Handler.dispatchMessage(Handler.java:99)
       at android.os.Looper.loop(Looper.java:176)
       at android.app.ActivityThread.main(ActivityThread.java:5317)
       at java.lang.reflect.Method.invokeNative(Method.java)
       at java.lang.reflect.Method.invoke(Method.java:511)
       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1102)
       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:869)
       at dalvik.system.NativeStart.main(NativeStart.java)
Caused by java.lang.NullPointerException
Caused by java.lang.NullPointerException
com.myApp.setAdapter (HackersProtected:32)
com.myApp.MyPage.onFragmentCreated (HackersProtected:165)
com.myApp.BaseFragment.onViewCreated (HackersProtected:105)
android.support.v4.app.FragmentManagerImpl.moveToState (HackersProtected:925)
android.support.v4.app.FragmentManagerImpl.moveToState (HackersProtected:1088)
android.support.v4.app.FragmentManagerImpl.moveToState (HackersProtected:1070)
android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated (HackersProtected:1861)
android.support.v4.app.Fragment.performActivityCreated (HackersProtected:1474)
android.support.v4.app.FragmentManagerImpl.moveToState (HackersProtected:931)
android.support.v4.app.FragmentManagerImpl.moveToState (HackersProtected:1088)
android.support.v4.app.FragmentManagerImpl.moveToState (HackersProtected:1070)
android.support.v4.app.FragmentManagerImpl.dispatchReallyStop (HackersProtected:1888)
android.support.v4.app.FragmentActivity.onReallyStop (HackersProtected:787)
android.support.v4.app.FragmentActivity.doReallyStop (HackersProtected:764)
android.support.v4.app.FragmentActivity.onDestroy (HackersProtected:322)
com.myApp.BaseActivity.onDestroy (HackersProtected:122)
android.app.Activity.performDestroy (Activity.java:434)
dalvik.system.NativeStart.main (NativeStart.java)