Fatal error: Uncaught Error: Class "Composer\Installers\BaseInstaller" not found in C:\Apache24\htdocs\cms_upgrade\vendor\composer\installers\src\Composer\Installers\TYPO3FlowInstaller.php:7 Stack trace: #0 {main} thrown in C:\Apache24\htdocs\cms_upgrade\vendor\composer\installers\src\Composer\Installers\TYPO3FlowInstaller.php on line 7