getNamedQuery returns null

I have a namedQuery that for some reason is returning null results from the database.

The namedQuery itself:

 @NamedQuery(name="Usuario.userLogin", query = "SELECT u.email, u.senha FROM Usuario u WHERE u.email = :mail AND u.senha = :senha")

The password is encrypted using md5 (not much use, but it is an academic work).

Implementing password decryption:

  response.setContentType("text/html;charset=UTF-8");
    PrintWriter pw = response.getWriter();
    String mail = request.getParameter("mail");        
    String senha = request.getParameter("senha");
    try {
        senha = ControllerUsuario.criptografa(senha);
    } catch (NoSuchAlgorithmException ex) {
        Logger.getLogger(CadastroUsuario.class.getName()).log(Level.SEVERE, null, ex);
    }
    Usuario user = ControllerUsuario.getSenha(mail, senha);
    if (user != null) {
        HttpSession session = request.getSession();
        pw.println("Tipo: " + user.getEmail());
        session.setAttribute("mail", user.getEmail());
        session.setAttribute("tipo_usr", user.getTipo_usr());
        session.setAttribute("usr", user.getUsuario());
        session.setAttribute("logado", 1);
      //  response.sendRedirect("index");
    } else {
        response.sendRedirect("cadastro-falha.html");
    } 
}

Implementation of getSenha

  public static Usuario getSenha(String mail, String senha) {
    SessionFactory sf = HibernateUtil.getSessionFactory();
    Session session = null;
    Transaction tx = null;
    Usuario user = new Usuario();
    try {
        session = sf.openSession();
        tx = session.getTransaction();
        tx.begin();
        Query query = session.getNamedQuery("Usuario.userLogin");
        query.setParameter("mail", mail);
        query.setParameter("senha", senha);
        user = (Usuario) query.uniqueResult();
        tx.commit();
    } catch (Exception e) {
        if (tx != null) tx.rollback();
    } finally {
        session.close();
    }
    return user;
}

What happens?