Fatal error: Uncaught Error: Interface "Symfony\Component\EventDispatcher\EventSubscriberInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/EventSubscriber/HtmlResponsePlaceholderStrategySubscriber.php:20 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/EventSubscriber/HtmlResponsePlaceholderStrategySubscriber.php on line 20