Fatal error: Uncaught Error: Class "Drupal\Component\Plugin\PluginManagerBase" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php:26 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Plugin/DefaultPluginManager.php on line 26