尝试调用虚拟方法'；void androidx.lifecycle.ViewModel.clear（）；关于空对象引用

因此，在我的应用程序Firebase Crashlytics的最后两个版本中，在androidX生命周期库的ViewModelStore类中报告了崩溃。我使用的生命周期库的版本是2.0.0。我在Google issue tracker上找不到与此相关的任何报告问题。以下是日志：

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.lifecycle.ViewModel.clear()' on a null object reference
   at androidx.lifecycle.ViewModelStore.clear(ViewModelStore.java:62)
   at androidx.fragment.app.FragmentManagerViewModel.clearNonConfigState(FragmentManagerViewModel.java:169)
   at androidx.fragment.app.FragmentStateManager.destroy(FragmentStateManager.java:480)
   at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1294)
   at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1354)
   at androidx.fragment.app.FragmentManager.moveFragmentToExpectedState(FragmentManager.java:1432)
   at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:442)
   at androidx.fragment.app.FragmentManager.executeOps(FragmentManager.java:2167)
   at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1990)
   at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
   at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1847)
   at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
   at android.os.Handler.handleCallback(Handler.java:789)
   at android.os.Handler.dispatchMessage(Handler.java:98)
   at android.os.Looper.loop(Looper.java:164)
   at android.app.ActivityThread.main(ActivityThread.java:6938)
   at java.lang.reflect.Method.invoke(Method.java)
   at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
   at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

有人知道什么是问题吗