我在android studio中创建了一个底部导航活动，并收到以下错误

Question

2019-12-12 17:34:34.470 31998-31998/com.example.givrish E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.givrish, PID: 31998
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.givrish/com.example.givrish.Dashboard}: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2827)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2905)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6591)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:857)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void androidx.appcompat.app.ActionBar.setTitle(java.lang.CharSequence)' on a null object reference
        at androidx.navigation.ui.ActionBarOnDestinationChangedListener.setTitle(ActionBarOnDestinationChangedListener.java:48)
        at androidx.navigation.ui.AbstractAppBarOnDestinationChangedListener.onDestinationChanged(AbstractAppBarOnDestinationChangedListener.java:100)
        at androidx.navigation.NavController.addOnDestinationChangedListener(NavController.java:218)
        at androidx.navigation.ui.NavigationUI.setupActionBarWithNavController(NavigationUI.java:220)
        at com.example.givrish.Dashboard.onCreate(Dashboard.java:26)
        at android.app.Activity.performCreate(Activity.java:7023)
        at android.app.Activity.performCreate(Activity.java:7014)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2780)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2905) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1631) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6591) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:857) 

这是我的密码

import android.os.Bundle;

import com.google.android.material.bottomnavigation.BottomNavigationView;

import androidx.appcompat.app.AppCompatActivity;
import androidx.navigation.NavController;
import androidx.navigation.Navigation;
import androidx.navigation.ui.AppBarConfiguration;
import androidx.navigation.ui.NavigationUI;

public class Dashboard extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_dashboard);
        BottomNavigationView navView = findViewById(R.id.nav_view);
        // Passing each menu ID as a set of Ids because each
        // menu should be considered as top level destinations.
        AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(
                R.id.navigation_home, 
                R.id.navigation_dashboard, 
                R.id.navigation_notifications)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment);
        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        NavigationUI.setupWithNavController(navView, navController);
    }

}