public void removeFormVotingUser(int userId, int formId) throws InvalidVotingUserException {
        try {
            String q = "delete from ValidVoter where formId = ? and userId = ?;";
            PreparedStatement st = conn.prepareStatement(q);
            st.setInt(1, formId);
            st.setInt(2, userId);
            st.executeUpdate();
            conn.commit();
        } catch(SQLException e) {
            try {
                conn.rollback();
            } catch(Exception e2) {
                e2.printStackTrace();
            }
            throw new InvalidVotingUserException();
        }
    }