I have an android app:
BaseDrawerActivity:
package com.HidiStudios.BeST;

import androidx.annotation.NonNull;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;

import android.content.Intent;
import android.view.MenuItem;

import com.google.android.material.navigation.NavigationView;

import java.util.Objects;

public abstract class BaseDrawerActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener {

    protected DrawerLayout drawerLayout;
    protected NavigationView navigationView;
    protected ActionBarDrawerToggle drawerToggle;

    // Initialize the drawer in the derived activity’s ‘onCreate’ method.
    protected void initializeDrawer() {
        drawerLayout = findViewById(R.id.drawer_layout);
        navigationView = findViewById(R.id.nav_view);
        drawerToggle = new ActionBarDrawerToggle(this, drawerLayout, R.string.open, R.string.close);
        drawerLayout.addDrawerListener(drawerToggle);
        drawerToggle.syncState();
        Objects.requireNonNull(getSupportActionBar()).setDisplayHomeAsUpEnabled(true);
        navigationView.setNavigationItemSelectedListener(this);
    }

    // Handle drawer item selected in one place.
    @Override
    public boolean onNavigationItemSelected(@NonNull MenuItem item) {
        // Your navigation item handling code…
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {
        if (drawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}

MainActivity:
[...]
public class MainActivity extends BaseDrawerActivity {
[...]
 @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // menuRelated
        initializeDrawer();


Activity_main.xml:
<?xml version="1.0" encoding="utf-8"?>

<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/drawer_layout"
    tools:context="com.HidiStudios.BeST.MainActivity">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.HidiStudios.BeST.MainActivity">


        <TextView
            android:id="@+id/Coins"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="50sp"
            android:text="@string/coins_message"
            android:textAlignment="center"
            android:textSize="20sp"
            android:textStyle="bold|italic" />

        <Button
            android:id="@+id/resetButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/RewardedbtnAds"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="-25dp"
            android:backgroundTint="@android:color/transparent"
            android:shadowColor="@color/black"
            android:shadowRadius="20"
            android:text="@string/reset_coins"
            android:textSize="4pt" />

        <Button
            android:id="@+id/IntbtnAds"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:backgroundTint="#DB4437"
            android:shadowColor="@color/black"
            android:shadowRadius="40"
            android:text="@string/load_interstitial_ad" />

        <Button
            android:id="@+id/BannerbtnAds"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_above="@+id/IntbtnAds"
            android:layout_centerHorizontal="true"
            android:layout_margin="50sp"
            android:backgroundTint="#4285F4"
            android:shadowColor="@color/black"
            android:shadowRadius="40"
            android:text="@string/toggle_banner_ad" />

        <Button
            android:id="@+id/RewardedbtnAds"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/IntbtnAds"
            android:layout_centerHorizontal="true"
            android:layout_margin="50sp"
            android:backgroundTint="#F4B400"
            android:shadowColor="@color/black"
            android:shadowRadius="40"
            android:text="@string/show_rewarded_ad" />

        <com.google.android.gms.ads.AdView
            xmlns:ads="http://schemas.android.com/apk/res-auto"
            android:id="@+id/adView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_alignParentBottom="true"
            ads:adSize="BANNER"
            ads:adUnitId="@string/BANNER_AD_UNIT_ID">
        </com.google.android.gms.ads.AdView>

    </RelativeLayout>

    <com.google.android.material.navigation.NavigationView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        app:headerLayout="@layout/header"
        app:menu="@menu/main_menu"
        android:id="@+id/nav_view"
        android:layout_gravity="start"
        />

</androidx.drawerlayout.widget.DrawerLayout>


main_menu.xml:
<?xml version="1.0" encoding="utf-8"?>

<androidx.drawerlayout.widget.DrawerLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:id="@+id/drawer_layout"
    tools:context="com.HidiStudios.BeST.MainActivity">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        tools:context="com.HidiStudios.BeST.MainActivity">


        <TextView
            android:id="@+id/Coins"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="50sp"
            android:text="@string/coins_message"
            android:textAlignment="center"
            android:textSize="20sp"
            android:textStyle="bold|italic" />

        <Button
            android:id="@+id/resetButton"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/RewardedbtnAds"
            android:layout_centerHorizontal="true"
            android:layout_marginTop="-25dp"
            android:backgroundTint="@android:color/transparent"
            android:shadowColor="@color/black"
            android:shadowRadius="20"
            android:text="@string/reset_coins"
            android:textSize="4pt" />

        <Button
            android:id="@+id/IntbtnAds"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerInParent="true"
            android:backgroundTint="#DB4437"
            android:shadowColor="@color/black"
            android:shadowRadius="40"
            android:text="@string/load_interstitial_ad" />

        <Button
            android:id="@+id/BannerbtnAds"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_above="@+id/IntbtnAds"
            android:layout_centerHorizontal="true"
            android:layout_margin="50sp"
            android:backgroundTint="#4285F4"
            android:shadowColor="@color/black"
            android:shadowRadius="40"
            android:text="@string/toggle_banner_ad" />

        <Button
            android:id="@+id/RewardedbtnAds"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_below="@+id/IntbtnAds"
            android:layout_centerHorizontal="true"
            android:layout_margin="50sp"
            android:backgroundTint="#F4B400"
            android:shadowColor="@color/black"
            android:shadowRadius="40"
            android:text="@string/show_rewarded_ad" />

        <com.google.android.gms.ads.AdView
            xmlns:ads="http://schemas.android.com/apk/res-auto"
            android:id="@+id/adView"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_centerHorizontal="true"
            android:layout_alignParentBottom="true"
            ads:adSize="BANNER"
            ads:adUnitId="@string/BANNER_AD_UNIT_ID">
        </com.google.android.gms.ads.AdView>

    </RelativeLayout>

    <com.google.android.material.navigation.NavigationView
        android:layout_width="wrap_content"
        android:layout_height="match_parent"
        app:headerLayout="@layout/header"
        app:menu="@menu/main_menu"
        android:id="@+id/nav_view"
        android:layout_gravity="start"
        />

</androidx.drawerlayout.widget.DrawerLayout>



How can I make it work?
Now, whenever I click the menu, the app crashes with NullPointer...