protected void onCreate(Bundle savedInstanceState)
    {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    ...
    firebaseAuth = new FirebaseAuth.getInstance();

在-> getInstance（）中获取错误

}
public void registerUser(){
... 
firebaseAuth.createUserWithEmailAndPassword(email,password)
            .addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
                @Override
                public void onComplete(@NonNull Task<AuthResult> task) {
                    if(task.isSuccessful()){
                        Toast.makeText(MainActivity.this,"Registered successfully",Toast.LENGTH_SHORT).show();
                    }else {Toast.makeText(MainActivity.this,"Registered unsuccessful",Toast.LENGTH_SHORT).show();}
                }
            });

我已经正确地将Firebase与我的项目同步，但出现此错误。