Fatal error: Uncaught Error: Class "Drupal\Core\Display\VariantBase" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Render/Plugin/DisplayVariant/SimplePageVariant.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Render/Plugin/DisplayVariant/SimplePageVariant.php on line 16