Getting NullPointerException on CacheFragmentStatePagerAdapter's restoreState when using nested fragments.

The setup for my current implementation looks like this:

• Activity
  • MainFragment
    • PagerFragment (with view pager)
      • ContentFragment

The error occurred when I was reloading fragments from my activity and did a setRestoreInstance(true) on the MainFragment. When the fragment is recreated that is when this following error occurs from the CacheFragmentStatePagerAdapter

java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2411) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2470) at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:4059) at android.app.ActivityThread.-wrap15(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5401) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:725) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:615) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'int java.util.ArrayList.size()' on a null object reference at android.support.v4.app.FragmentManagerImpl.getFragment(FragmentManager.java:587) at com.github.ksoichiro.android.observablescrollview.CacheFragmentStatePagerAdapter.restoreState(CacheFragmentStatePagerAdapter.java:75) at android.support.v4.view.ViewPager.onRestoreInstanceState(ViewPager.java:1318) at android.view.View.dispatchRestoreInstanceState(View.java:14669)

the error occurs on this line in the CacheFragmentPagerAdapter

Fragment f = this.mFm.getFragment(bundle, this.createCacheKey(position));