Fatal error: Uncaught Error: Class 'Symfony\Component\Validator\Constraint' not found in /home/soh-works/www/3good_old/vendor/symfony/validator/Constraints/Isbn.php:24 Stack trace: #0 {main} thrown in /home/soh-works/www/3good_old/vendor/symfony/validator/Constraints/Isbn.php on line 24