Fatal error: Uncaught Error: Class "Symfony\Component\Config\Definition\Builder\NodeDefinition" not found in /opt/lampp/htdocs/forum/flarum/vendor/symfony/config/Definition/Builder/VariableNodeDefinition.php:21 Stack trace: #0 {main} thrown in /opt/lampp/htdocs/forum/flarum/vendor/symfony/config/Definition/Builder/VariableNodeDefinition.php on line 21