Fatal error: Uncaught Error: Interface "Drupal\Core\Render\PlaceholderGeneratorInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Render/PlaceholderGenerator.php:13 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Render/PlaceholderGenerator.php on line 13