java.lang.NullPointerException

java.lang.NullPointerException: Attempt to read from field 'float com.github.florent37.materialviewpager.MaterialViewPagerAnimator.lastYOffset' on a null object reference at com.github.florent37.materialviewpager.MaterialViewPager.onSaveInstanceState(MaterialViewPager.java:123) at android.view.View.dispatchSaveInstanceState(View.java:15688) at android.view.ViewGroup.dispatchSaveInstanceState(ViewGroup.java:3206) at android.view.ViewGroup.dispatchSaveInstanceState(ViewGroup.java:3212) at android.view.View.saveHierarchyState(View.java:15671) at androidx.fragment.app.FragmentManagerImpl.saveFragmentViewState(FragmentManagerImpl.java:2276) at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:951) at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1238) at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:434) at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2079) at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1869) at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1824) at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1727) at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150) at android.os.Handler.handleCallback(Handler.java:751) at android.os.Handler.dispatchMessage(Handler.java:95) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)