解决Fail to post notification on channel "null"的方法

mNotifyMgr = (NotificationManager) getSystemService(NOTIFICATION_SERVICE);
mNotifyMgr.cancelAll();

String title = getString(R.string.filtershow_notification_label);
        if(Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
            String id = "channel_1";
            NotificationChannel channel = new NotificationChannel(id, title, NotificationManager.IMPORTANCE_HIGH);
            mNotifyMgr.createNotificationChannel(channel);
            mBuilder = new Notification.Builder(this, id)
                    .setCategory(Notification.CATEGORY_EVENT)
                    .setSmallIcon(R.drawable.filtershow_button_fx)
                    .setContentTitle(title)
                    .setContentText(getString(R.string.filtershow_notification_message))
                    .setAutoCancel(true);
        } else {
            mBuilder = new Notification.Builder(this)
                    .setSmallIcon(R.drawable.filtershow_button_fx)
                    .setContentTitle(title)
                    .setContentText(getString(R.string.filtershow_notification_message));
        }

mNotifyMgr.notify(mNotificationId, mBuilder.build());