Check for Firebase node

Question

Good afternoon, I am checking if there is a node in Firebase, if it exists I will just increment the value on that node, but when it does not exist I will create the node, but Else is not working. If this is the first time the user will register a monthly expense, the node month/year will not exist yet, then I need to create it, and the next times the node will already be created, then I only increase with the value that is already registered.

public void atualizarDespesaMensal(Double despesaMes, Double valorDigitado,String mesAno){

        //Recuperamos o email do usuario logado
        String emailUsuario = autenticacao.getCurrentUser().getEmail();
        //codificamos usando a classe Base64Custom
        String idUsuario = Base64Custom.codificarBase64(emailUsuario);

        movimentacaoSaldoMensalRef = firebaseRef.child("saldoMensal")
                .child(idUsuario);                    

        valueEventListenerAtualizarDespesaMensal = movimentacaoSaldoMensalRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
              

                if (snapshot.child(mesAno).exists()) {
                    Log.i("IF", "O nó existe, vamos incrementa o valor"); //IF FUNCIONA
                    
                }else{
                    Log.i("ELSE", "Se o nó não existir irei criar"); //NO ELSE NÃO FUNCIONA
                }   

            }

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

            }
        });
    }

Answer 1

try using firebase increment.

movimentacaoSaldoMensalRef = firebaseRef.child("saldoMensal")
    .child(idUsuario)
    .set(firebase.database.ServerValue.increment(valor))

this method increments if the node already has a value and creates if it does not exist. remember that this calculation is performed on the server. and not on the client.