Fatal error: Uncaught Error: Interface "Drupal\Component\Render\OutputStrategyInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Component/Render/PlainTextOutput.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Component/Render/PlainTextOutput.php on line 16