Making an android module always crash

Question

I am new to Godot and I am following the tutorial to add custom function on Android.
https://docs.godotengine.org/en/3.1/development/cpp/creating_android_modules.html

After I add custom code (same as the tutorial), the app crash with the following error.

--------- beginning of crash
2020-02-25 10:54:44.774 927-927/org.godotengine.character E/AndroidRuntime: FATAL EXCEPTION: main
    Process: org.godotengine.character, PID: 927
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{org.godotengine.character/com.godot.game.GodotApp}: java.lang.InstantiationException: java.lang.Class<com.godot.game.GodotApp> has no zero argument constructor
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3340)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3594)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2146)
        at android.os.Handler.dispatchMessage(Handler.java:107)
        at android.os.Looper.loop(Looper.java:237)
        at android.app.ActivityThread.main(ActivityThread.java:7762)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1047)
     Caused by: java.lang.InstantiationException: java.lang.Class<com.godot.game.GodotApp> has no zero argument constructor
        at java.lang.Class.newInstance(Native Method)
        at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
        at android.support.v4.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:43)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1251)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3328)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3594) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2146) 
        at android.os.Handler.dispatchMessage(Handler.java:107) 
        at android.os.Looper.loop(Looper.java:237) 
        at android.app.ActivityThread.main(ActivityThread.java:7762) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1047) 

This is the code I added (copy and paste A singleton object template):

public class GodotApp extends Godot.SingletonBase {

    protected Activity appActivity;
    protected Context appContext;
    private int instanceId = 0;

    public int myFunction(String p_str) {
        // a function to bind
        return 1;
    }

    public void getInstanceId(int pInstanceId) {
        // You will need to call this method from Godot and pass in the get_instance_id().
        instanceId = pInstanceId;
    }

    static public Godot.SingletonBase initialize(Activity p_activity) {
        return new GodotApp(p_activity);
    }

    public GodotApp(Activity p_activity) {
        //register class name and functions to bind
        registerClass("MySingleton", new String[]
                {
                        "myFunction",
                        "getInstanceId"
                });
        this.appActivity = p_activity;
        this.appContext = appActivity.getApplicationContext();
        // you might want to try initializing your singleton here, but android
        // threads are weird and this runs in another thread, so to interact with Godot you usually have to do
        appActivity.runOnUiThread(new Runnable() {
            public void run() {
                //useful way to get config info from project.godot
                String key = GodotLib.getGlobal("plugin/api_key");
                //SDK.initializeHere();
            }
        });

    }

    // forwarded callbacks you can reimplement, as SDKs often need them

    protected void onMainActivityResult(int requestCode, int resultCode, Intent data) {}
    protected void onMainRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults) {}

    protected void onMainPause() {}
    protected void onMainResume() {}
    protected void onMainDestroy() {}

    protected void onGLDrawFrame(GL10 gl) {}
    protected void onGLSurfaceChanged(GL10 gl, int width, int height) {} // singletons will always miss first onGLSurfaceChanged call

}

Before I add any code on Java file, it runs no problem.
It can also run on PC smoothly.
My configuration:

• Android: Android Studio 3.5.3
• NDK(side by side): 21.0.6113669
• Java: jdk-12.0.2
• Phone: Samsung Galaxy S10 with Android 10.
• The app is run by connecting my phone via USB cable and pressing Android icon on the top-right corner.

Thank you for your patient.