Fatal error: Uncaught Error: Interface "Drupal\Core\Config\Entity\ConfigEntityInterface" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Datetime/DateFormatInterface.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Datetime/DateFormatInterface.php on line 10