HMVC | Undefined property: $session | $this->session is null

[eluser]oukarai[/eluser]
hi

i got this erro message:

A PHP Error was encountered
Severity: Notice
Message: Undefined property: Login::$session
Filename: controllers/login.php

and my login control is

login.php

class Login extends CI_Controller
{
function is_logged_in()
{
$is_logged_in = $this->session->userdata('is_logged_in'); //<=here

if(!isset($is_logged_in) || $is_logged_in != true) {

echo 'You don\'t have permission to access this page.';

die();
}
}
}

and my site control is

class Site extends CI_Controller
{
function __construct()
{
parent::__construct();

modules::run('login/is_logged_in');
}

function members_area()
{
$this->load->view('logged_in_area');
}
}

while its only one part of the source

i access http://localhost/hmvcExample/index.php/s...mbers_area

the error message is showed

i haved autoload libraries session

help!!!