How to use MY_controller with ci 2.0

[eluser]chefnelone[/eluser]
I used to use MY_controller in this way in ci 1.7 but isn't working in ci 2.0
No error message, just a blank page...

In a fresh ci installation:
application/controller/welcome.php

Code:

<?php if ( ! defined('BASEPATH')) exit('No direct script access allowed');

class Welcome extends MY_Controller{

    function __construct()
    {
        parent::__construct();
    }

    function index()
    {
        $this->load->view('welcome_message');
    }
}

/* End of file welcome.php */
/* Location: ./application/controllers/welcome.php */

library/MY_controller.php

Code:

<?php if (!defined('BASEPATH')) exit('No direct script access allowed');

    class  MY_Controller extends CI_Controller{
    
    
        function __construct(){        
        


        }

}

What am I missing?
Thanks