get_instance return null

Hi friends.

I have started migrating some projects in CI2 to CI3 but it crashed in a simply thing.

if I create my extension core for Exceptions:

/application/core/MY_Exceptions.php:

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

class MY_Exceptions extends CI_Exceptions
{
    private $_ci;

    public function __construct()
    {
        parent::__construct();
        $this->_ci = &get_instance();
        
        var_dump($this->_ci);
    }
}

It returns NULL  all the time.

I am doing something simple wrong but I don't know what.

Any help?

echo 'Thanks';