Ошибка приложения вылетает как исправить?

Question

[EgorItChainik]

Прописал код для приема и передачи текстовых данных из firebase.
Вот ошибка:

FATAL EXCEPTION: main
    Process: anonimchatguest.app, PID: 32538
    com.google.firebase.database.DatabaseException: Failed to convert value of type java.util.HashMap to String
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertString(CustomClassMapper.java:426)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(CustomClassMapper.java:217)
        at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(CustomClassMapper.java:80)
        at com.google.firebase.database.DataSnapshot.getValue(DataSnapshot.java:203)
        at anonimchatguest.app.ChatActivity$1.onChildAdded(ChatActivity.java:71)
        at com.google.firebase.database.core.ChildEventRegistration.fireEvent(ChildEventRegistration.java:79)
        at com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63)
        at com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:236)
        at android.app.ActivityThread.main(ActivityThread.java:8056)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:656)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:967)

Синим отмечена вот эта строчка:

String msg=snapshot.getValue(String.class);

Вот код данного активити полностью

public class ChatActivity extends AppCompatActivity {
    private EditText edit_chat;
    private ImageView image_go_message,imageView_dialog;
    private Dialog chatdialog;
    private DatabaseReference databaseReference;
private EditText textget;
    private FirebaseAuth mAuth;

private RecyclerView recycle;
private ArrayList<String> messages=new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_chat);
        edit_chat=(EditText) findViewById(R.id.edit_chat);
        imageView_dialog=(ImageView) findViewById(R.id.imageView_dialog);
        image_go_message=(ImageView) findViewById(R.id.image_go_message);
        mAuth = FirebaseAuth.getInstance();
        textget=(EditText) findViewById(R.id.textget);
        databaseReference = FirebaseDatabase.getInstance().getReference().child("User").child("d");
Adapter adapter=new Adapter(this,messages);
        recycle=(RecyclerView) findViewById(R.id.recycle);


        recyclemanwoman.setLayoutManager(new LinearLayoutManager(this));

        ///adapter///
        recycle.setAdapter(adapter);


chatdialog=new Dialog(ChatActivity.this);

        databaseReference.addChildEventListener(new ChildEventListener() {
            @Override
            public void onChildAdded(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {
                String msg=snapshot.getValue(String.class);
                messages.add(msg);
                adapter.notifyDataSetChanged();
                recycle.smoothScrollToPosition(messages.size());
            }

            @Override
            public void onChildChanged(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

            }

            @Override
            public void onChildRemoved(@NonNull DataSnapshot snapshot) {

            }

            @Override
            public void onChildMoved(@NonNull DataSnapshot snapshot, @Nullable String previousChildName) {

            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {

            }
        });

        imageView_dialog.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                chatdialogShow();
            }
        });
        image_go_message.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                ValidateAndSaveOnlyInfo();
            }

        });

    }

    private void chatdialogShow() {
        chatdialog.setContentView(R.layout.dialog_exit);
        chatdialog.getWindow().setBackgroundDrawable(new ColorDrawable(Color.TRANSPARENT));
        Button button_chat_end=chatdialog.findViewById(R.id.button_chat_end);
        Button button_back_chat=chatdialog.findViewById(R.id.button_back_chat);

        button_back_chat.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                chatdialog.dismiss();
            }
        });
        button_chat_end.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {

            }
        });
        chatdialog.show();
    }
    private void ValidateAndSaveOnlyInfo() {
        if (TextUtils.isEmpty(edit_chat.getText().toString())) {
            Toast.makeText(this, "Введите текст", Toast.LENGTH_SHORT).show();

        } else {
            HashMap<String, Object> userMap = new HashMap<>();
            userMap.put("uid", mAuth.getCurrentUser().getUid());
            userMap.put("text", edit_chat.getText().toString());


            databaseReference.child(mAuth.getCurrentUser().getUid()).updateChildren(userMap);

            edit_chat.setText("");
        }

    }

}

В чем ошибка,и почему ее видно только в Logcat?