Fatal error: Uncaught Error: Class "Symfony\Component\Config\Definition\Exception\Exception" not found in C:\Apache24\htdocs\cms_upgrade\vendor\symfony\config\Definition\Exception\UnsetKeyException.php:20 Stack trace: #0 {main} thrown in C:\Apache24\htdocs\cms_upgrade\vendor\symfony\config\Definition\Exception\UnsetKeyException.php on line 20