Fatal error: Uncaught Error: Class "Drupal\Core\Render\Element\RenderElement" not found in /home/www/drupal8/test/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/contextual/src/Element/ContextualLinksPlaceholder.php on line 16