Why the value of the retrieved from the Firebase Realtime database data is null?

Question

I am trying to get values of child 'class_password' & 'class_uuid', but it always gives me a null value. Why is it so?

Firebase Realtime database

Here is the code :

public class StudentJoinClassDialog {
    Context context;
    Dialog dialog;
    TextInputEditText classCode, classPassword;
    Button studentJoinClass;
    String selectedClasscode, selectedClassPass;
    String checkPassword, checkClassUuid;
    String TAG = "StudentJoinClassDialog";

    public StudentJoinClassDialog(@NonNull Context mContext) {
        this.context = mContext;
        dialog = new Dialog(context);

    }

    public void showDialog() {
        dialog.setContentView(R.layout.student_join_class_dialog_layout);
        dialog.getWindow().setBackgroundDrawable(new ColorDrawable(android.R.attr.colorBackground));
        dialog.create();
        dialog.show();

        // IDs //
        classCode = dialog.findViewById(R.id.enter_class_code_input_edit_text);
        classPassword = dialog.findViewById(R.id.enter_class_password_inputedittext);
        studentJoinClass = dialog.findViewById(R.id.join_class_btn);
        // IDs //**

        studentJoinClass.setOnClickListener(view -> {
            selectedClassPass = classPassword.getEditableText().toString().trim();

            Log.d(TAG, "class UUID : " + selectedClasscode + " class Password : " + selectedClassPass);
            Log.d(TAG, "classbook path : " + "classbook " + "/" + selectedClasscode + "/" + "class_information");

            FirebaseDatabase
                    .getInstance()
                    .getReference()
                    .child("classbook")
                    .child(classCode.getEditableText().toString().trim())
                    .child("class_information")
                    .addValueEventListener(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot snapshot) {
                            checkClassUuid = snapshot.child("class_uuid").getValue(String.class);
                            checkPassword = snapshot.child("class_password").getValue(String.class);
                            if (selectedClasscode.equals(checkClassUuid) && selectedClassPass.equals(checkPassword)) {
                                Toast.makeText(context, "You are in", Toast.LENGTH_LONG).show();
                            } else {
                                Toast.makeText(context, "Class does not exist", Toast.LENGTH_SHORT).show();
                            }
                        }

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

                        }
                    });
            Log.d(TAG, "Retrieved Class UUID : " + checkClassUuid + " Retrieved Class Password : " + checkPassword);
        });
    }
}

Log :

2021-11-06 20:32:33.409 8071-8071/com.vrs.attendy D/StudentJoinClassDialog: class UUID : null class Password : 123 2021-11-06 20:32:33.409 8071-8071/com.vrs.attendy D/StudentJoinClassDialog: classbook path : classbook /null/class_information 2021-11-06 20:32:33.409 8071-8071/com.vrs.attendy D/StudentJoinClassDialog: Retrieved Class UUID : null Retrieved Class Password : null