When there is no entry in database, if (dataSnapshot.getValue() == null) returns true but also run the else part after finishing the "if" part

Question

I have a register page in my app, and while registering, i check if the name is already registered or not in firebase. And if the name is already present, I am getting the toast message("user already exist") as required, but if there is a new entry, I am able to register perfectly but I am also getting the toast message after registration.

Please refer the below code:

mFirebaseDatabase = FirebaseDatabase.getInstance().getReference().child("Registration");

mFirebaseDatabase.orderByChild("uname").
equalTo(name.getSelectedItem().toString().trim()).addValueEventListener(new ValueEventListener() {            

    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
        if (dataSnapshot.getValue() == null) {
            if (TextUtils.isEmpty(userId)) {
                createUser(name.getSelectedItem().toString().trim(), 
                           designation.getSelectedItem().toString().trim(),
                           phone.getText().toString().trim(), 
                           email.getText().toString().trim(),
                           password.getText().toString().trim(),
                           email1.getText().toString().trim(),
                           phone1.getText().toString().trim(),
                           telephone.getText().toString().trim());
                 Intent login = new Intent(Register.this, Login.class);
                 startActivity(login);
             }
         } else {
             Toast.makeText(Register.this, "User already Registered", Toast.LENGTH_SHORT).show();
         }
     }

     @Override
     public void onCancelled(@NonNull DatabaseError databaseError) {}
 });

So After registration, I am getting the message "user already registered"