Multiple Applications

Hello there...
I try to setup multiple applications and I followed the instructions on http://codeigniter.com/user_guide/genera..._apps.html .
The only thing I had to change was in this file: 

Code:

mySubFolder/app/Config/Paths.php

There I change one row from:

PHP Code:

public $systemDirectory = __DIR__ . '/../../vendor/codeigniter4/framework/system'; 


to

PHP Code:

public $systemDirectory = __DIR__ . '/../../../vendor/codeigniter4/framework/system'; 


...and it works.

Now I want to have composer-support and I change in the file:

Code:

mySubFolder/app/Config/Constants.php

the row

PHP Code:

defined('COMPOSER_PATH') || define('COMPOSER_PATH', ROOTPATH . 'vendor/autoload.php'); 


to

PHP Code:

defined('COMPOSER_PATH') || define('COMPOSER_PATH', ROOTPATH . '../vendor/autoload.php'); 


like explained in the guide.
But then I get following error:

Code:

Fatal error: Uncaught TypeError: Argument 1 passed to CodeIgniter\CodeIgniter::__construct() must be an instance of Config\App, null given, called in C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\Config\Services.php on line 139 and defined in C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\CodeIgniter.php:147 Stack trace: #0 C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\Config\Services.php(139): CodeIgniter\CodeIgniter->__construct(NULL) #1 C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\Config\BaseService.php(248): CodeIgniter\Config\Services::codeigniter(NULL, false) #2 C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\Config\BaseService.php(189): CodeIgniter\Config\BaseService::__callStatic('codeigniter', Array) #3 C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\Config\Services.php(134): CodeIgniter\Config\BaseService::getSharedInstance('co in C:\xampp\htdocs\kighwebapps\ci4-projects\vendor\codeigniter4\framework\system\CodeIgniter.php on line 147

How could I fix this error ?!?