Fatal error: Uncaught Error: Class "Symfony\Component\Mime\Header\AbstractHeader" not found in /opt/lampp/htdocs/forum/flarum/vendor/symfony/mime/Header/DateHeader.php:19 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/forum/flarum/vendor/symfony/mime/Header/DateHeader.php on line 19