Fatal error: Uncaught Error: Class "Drupal\Core\Plugin\PluginBase" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Entity/EntityReferenceSelection/SelectionPluginBase.php:14 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Entity/EntityReferenceSelection/SelectionPluginBase.php on line 14