ID by variable it returns null and if you put the ID "in hand" it returns the right object

Question

I am trying to recover a code received by a request to recover objects from the database, but am encountering some problems.

Performing tests, replace the id coming from the request, by a forced value ("written in the hand") and managed to obtain the object.

Follows my code:

List<String> codigos = new ArrayList<>();


String idPeca = request.getParameter("idPeca");
ControlePeca cp = new ControlePeca();
for (Peca p1 : cp.buscarPecas(Peca.class)) {
    codigos.add(p1.getIdPeca());
}

for (String id : codigos) {
    System.out.println(id); //sai o id que, é o mesmo contigo em idPeca
    System.out.println(cp.buscarPorId(id)); //traz o objeto que tem o id
    System.out.println(cp.buscarPorId(idPeca)); //traz null
}


    Query query = session.createQuery(hql);
    query.setMaxResults(1);
    Peca peca = (Peca) query.uniqueResult();
    session.clear();
    session.close();
    return peca;
}

I have a class Pecadao that is called by the controller Controlepeca()

This is the method I tested by forcing the data. If I replace the id with a string in the database it returns correct, but not the variable.

public Peca buscarPorId(String id) {
    Session session = HibernateUtil.getSessionFactory().openSession();
    String hql = "from peca p where p.id = '" + **id** + "' "; 
}

I would like to know why this search returns null just by coming from request.getParameter Obs: I have already checked if the value coming from the request has in the bank, and yes it has;