Fatal error: Uncaught Error: Interface "Symfony\Component\Serializer\Mapping\ClassDiscriminatorResolverInterface" not found in /srv/disk1/2895578/www/whittonphotographicclub.org.uk/concrete/vendor/symfony/serializer/Mapping/ClassDiscriminatorFromClassMetadata.php:19 Stack trace: #0 {main} thrown in /srv/disk1/2895578/www/whittonphotographicclub.org.uk/concrete/vendor/symfony/serializer/Mapping/ClassDiscriminatorFromClassMetadata.php on line 19