Fatal error: Uncaught Error: Class "Symfony\Component\Validator\Constraint" not found in /home/qcsvlel/www/core/lib/Drupal/Core/Extension/Plugin/Validation/Constraint/ExtensionExistsConstraint.php:18 Stack trace: #0 {main} thrown in /home/qcsvlel/www/core/lib/Drupal/Core/Extension/Plugin/Validation/Constraint/ExtensionExistsConstraint.php on line 18