调用Handler.sendEmptyMessageDelayedint，long时发生NullPointerException

如何解决调用Handler.sendEmptyMessageDelayedint，long时发生NullPointerException

最近发布应用后，在Crashlytics中看到了该崩溃。它在后台发生100％；索尼有50％，华为/小米有50％，三星没有。在Android 10中为79％，在Android 8中为19％。

Fatal Exception: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.os.Handler.sendEmptyMessageDelayed(int,long)' on a null object reference
       at xxx.xxx.xxx.MyEventManager$MyHandler.handleMessage(MyEventManager.java:80)
       at android.os.Handler.dispatchMessage(Handler.java:107)
       at android.os.Looper.loop(Looper.java:359)
       at android.os.HandlerThread.run(HandlerThread.java:67)

代码段：

public class MyEventManager {

    private static class SingletonInstance {
        private static final MyEventManager INSTANCE = new MyEventManager();
    }

    public static MyEventManager getInstance() {
        return SingletonInstance.INSTANCE;
    }

    private HandlerThread mHandlerThread;
    private Handler mHandler;

    private class MyHandler extends Handler {

        public MyHandler(@NonNull Looper looper) {
            super(looper);
        }

        @Override
        public void handleMessage(@NonNull Message message) {
            super.handleMessage(message);

            switch (message.what) {
                case ACTION_SEND_REQUEST:
                    if (isThreadReady()) {
                        queryDatabaseAndSendRequest();
                        mHandler.sendEmptyMessageDelayed(ACTION_SEND_REQUEST,600 * 1000);
                    }
                    break;

                default:
                    break;
            }
        }
    }

    private boolean isThreadReady() {
        return mHandler != null && mHandlerThread != null && mHandlerThread.getState() != Thread.State.TERMINATED;
    }

    private void initHandlerThreadIfNeeded() {
        if (!isThreadReady()) {
            mHandlerThread = new HandlerThread(TAG_HANDLER);
            mHandlerThread.start();

            mHandler = new MyHandler(mHandlerThread.getLooper());
        }
    }

    public void stopAll() {
        if (mHandler != null) {
            mHandler.removeCallbacksAndMessages(null);
            mHandler = null;
        }

        if (mHandlerThread != null) {
            mHandlerThread.quit();
            mHandlerThread = null;
        }
    }

}

类itemReader.setRecordSeparatorPolicy(new DefaultRecordSeparatorPolicy()); 定期向服务器发送一些数据；从代码段中可以看到，它在MyEventManager中调用mHandler.sendEmptyMessageDelayed()安排下一个触发器。

在handleMessage()的{​​{1}}中调用方法stopAll()。

由于它是在后台100％发生的，并且MainActivity在onDestroy()中设置为null，所以我认为mHandler当时已被销毁，但这很奇怪，因为任何待处理的消息应该会在调用stopAll()时被MainActivity删除，此外，在调用mHandler.removeCallbacksAndMessages(null)之前存在空检查。

谁能告诉我为什么我要获得NPE？