迁移到 AndroidX 后，应用程序崩溃并尝试在空引用上调用 androidx.fragment.app.FragmentManagerImpl.isDestroyed()

完整的堆栈仅包括 android 核心代码：

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean androidx.fragment.app.FragmentManagerImpl.isDestroyed()' on a null object reference
    at androidx.fragment.app.Fragment.performDetach(Fragment.java:2844)
    at androidx.fragment.app.FragmentManagerImpl.moveToState(FragmentManagerImpl.java:1033)
    at androidx.fragment.app.FragmentManagerImpl.moveFragmentToExpectedState(FragmentManagerImpl.java:1237)
    at androidx.fragment.app.BackStackRecord.executeOps(BackStackRecord.java:434)
    at androidx.fragment.app.FragmentManagerImpl.executeOps(FragmentManagerImpl.java:2075)
    at androidx.fragment.app.FragmentManagerImpl.executeOpsTogether(FragmentManagerImpl.java:1865)
    at androidx.fragment.app.FragmentManagerImpl.removeRedundantOperationsAndExecute(FragmentManagerImpl.java:1820)
    at androidx.fragment.app.FragmentManagerImpl.execPendingActions(FragmentManagerImpl.java:1726)
    at androidx.fragment.app.FragmentManagerImpl$2.run(FragmentManagerImpl.java:150)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:193)
    at android.app.ActivityThread.main(ActivityThread.java:6669)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)

当替换主活动中的片段时会发生这种情况：

Runnable mPendingRunnable = new Runnable() {
            @Override
            public void run() {
                FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
                fragmentTransaction.replace(R.id.frame, fragment);
                fragmentTransaction.commitAllowingStateLoss();
            }
        };

我在 myFragment.onDetach 中发现了一段导致此问题的代码：

这是一个解决方法在 ViewPager 中使用选项卡时出现错误“Java.lang.IllegalStateException Activity has been destroy” https://stackoverflow.com/questions/15207305/getting-the-error-java-lang-illegalstateexception-activity-has-been-destroyed

        try {
            Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
            childFragmentManager.setAccessible(true);
            childFragmentManager.set(this, null);
        } catch (NoSuchFieldException e) {
            throw new RuntimeException(e);
        } catch (IllegalAccessException e) {
            throw new RuntimeException(e);
        }

现在，在 androidx 中，不需要此解决方法。