添加Bottom Navigation Activity后编译出错（非法字符）

添加底部导航活动并尝试从另一个活动调用它后，在编译时出现错误：

{project directory}\ui\dashboard\DashboardFragment.java:13: error: illegal character: '`'
import `in`.ac.somedomain.someappname.R;

导致错误的 DashboardFragment.java 中的代码是导入行：

import `in`.ac.somedomain.someappname.R;

我只添加了一个新的底部导航活动，并尝试使用以下方法调用它：

Intent homeIntent = new Intent(getApplicationContext, HomeActivity.class);
startActivity(homeIntent);

在手动删除“`”时（在 3 个活动中：DashboardFragment、HomeFragment、NotificationsFragment），调用活动时发生以下错误（logcat，应用程序崩溃）：

2020-05-24 16:29:02.711 14323-14323/in.ac.somedomain.someappname E/AndroidRuntime: FATAL EXCEPTION: main
    Process: in.ac.somedomain.someappname, PID: 14323
    java.lang.RuntimeException: Unable to start activity ComponentInfo{in.ac.somedomain.someappname/in.ac.somedomain.someappname.BaseActivity}: 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:2943)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3078)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6854)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:860)
     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 in.ac.somedomain.someappname.BaseActivity.onCreate(BaseActivity.java:26)
        at android.app.Activity.performCreate(Activity.java:7151)
        at android.app.Activity.performCreate(Activity.java:7142)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2923)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3078) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6854) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:860) 

将鼠标悬停在代码中的“`in`”上时出现错误Raw string literals are not supported at language level '7'，我尝试了它的一些建议（将源兼容性切换为 1.8，这与级别 8 相同），禁用了一些没有改变任何东西的东西，并且现在它只是告诉我去模块设置，但我怀疑原始字符串是问题所在。

我该怎么做才能使我的底部导航活动正常工作？

编辑：活动代码（底部导航活动，称为 Main2Activity）：

package in.ac.somedomain.somename;

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 Main2Activity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);
        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);
//the below line was causing the problem
//        NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
        NavigationUI.setupWithNavController(navView, navController);
    }

}