String sql = "SELECT id_usuario,nome,senha FROM usuario where login = ? and senha = ?";
    try {
        PreparedStatement stmt = con.prepareStatement(sql);
        stmt.setString(1, u.getLogin());
        stmt.setString(2, u.getSenha());
        ResultSet rs = stmt.executeQuery();

if (rs.next()){
            String update = "UPDATE usuario SET senha=? WHERE id_usuario = " +Sessao.getInstancia().getUsuario().getId()+ "";
            PreparedStatement stmt2 = con.prepareStatement(sql);
            stmt2.setString(1, u.getNovaSenha());
            ResultSet rs2 = stmt2.executeQuery();

            return true;
        }

GRAVE: null
java.sql.SQLException: No value specified for parameter 2