Steps to reproduce the issue

Install an extension running on J 3.8 that extends JControllerLegacy and override the constructor __construct

Expected result

All works fine

Actual result

Fatal error: Call to a member function createModel() on null in E:\vhosts\joomla39\libraries\src\MVC\Controller\BaseController.php on line 559

System information (as much as possible)

With the current MVC backported from J4.0 now a class that extends JControllerLegacy AKA Joomla\CMS\MVC\Controller\BaseController throws a fatal error if there is an override for the constructor and the property 'factory' is so empty

Additional comments

Check the existance of the factory object before calling:
$this->factory->createModel
$this->factory->createView