No output using CLI with CodeIgniter

I'm making a Cron job in CodeIgniter and I need access to my models in order to perform it's tasks. Here's my controller code.

PHP Code:

<?php
    class Cron extends CI_Controller
    {
    public function send_mail() {
    if ( PHP_SAPI !== 'cli' ) exit('No web access allowed');
            echo "Hello World";
    }
 } 


And if I run this command on the terminal

Code:

php /home/path/to/project/index.php cron send_mail

It doesn't return anything, it's not executing the function. But if I delete the database and session libraries from the autoload.php file, it runs perfectly. Any ideas?