当我点击注销时，我的应用程序崩溃

我有一个允许我登录和退出的应用程序。注销按钮现在似乎使应用程序崩溃，当我以前工作正常时按下它。它仍然会注销用户，当您返回应用程序时，您必须再次登录。

我在下面的 create 方法中添加了我的全部内容，操作发生在底部。以防万一我添加了重复项或我遗漏的东西

 //view objects
    private TextView textViewUserEmail;
    private Button buttonLogout;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_profile);

        buttonAddProducts = (Button) findViewById(R.id.buttonAddProducts);
        buttonAddBeverages = (Button) findViewById(R.id.buttonAddBeverages);
        buttonLogout = (Button) findViewById(R.id.buttonLogout);
        firebaseAuth = FirebaseAuth.getInstance();
        buttonAddProducts.setVisibility(View.GONE);
        buttonAddBeverages.setVisibility(View.GONE);

        databaseUsers = FirebaseDatabase.getInstance().getReference("users");

        String uid = FirebaseAuth.getInstance().getCurrentUser().getUid();
        DatabaseReference currentUserReference = databaseUsers.child(uid);
        currentUserReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot userSnapshot) {
                if (userSnapshot.exists()) {
                    User user = userSnapshot.getValue(User.class);

                    if(user.getAdminUser() == true)
                    {
                        buttonAddProducts.setVisibility(View.VISIBLE);
                        buttonAddBeverages.setVisibility(View.VISIBLE);
                    }
                }
                else{
                    Log.i("myInfoTag", "Connection problem");
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                throw databaseError.toException(); // don't ignore exceptions
            }
        });


        //if the user is not logged in
        //that means current user will return null
        if(firebaseAuth.getCurrentUser() == null){
            //closing this activity
            finish();
            //starting login activity
            startActivity(new Intent(this, LoginActivity.class));
        }

        //getting current user
        FirebaseUser user = firebaseAuth.getCurrentUser();

        //initializing views
        textViewUserEmail = (TextView) findViewById(R.id.textViewUserEmail);


        //displaying logged in user name
        textViewUserEmail.setText("Welcome "+user.getEmail());


        buttonLogout.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //logging out the user
                firebaseAuth.signOut();
                //closing activity
                finish();
                //starting login activity
                startActivity(new Intent(ProfileActivity.this, SignUpActivity.class));
            }
        });


    }

当我按下注销时，它只是崩溃，味精啤酒应用程序已停止