Fatal error: Uncaught Error: Class "Drupal\Core\Entity\EntityReferenceSelection\SelectionPluginBase" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Entity/Plugin/EntityReferenceSelection/DefaultSelection.php:39 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Entity/Plugin/EntityReferenceSelection/DefaultSelection.php on line 39