Fatal error: Uncaught Error: Interface "Drupal\Core\Render\MainContent\MainContentRendererInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php:31 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php on line 31