Fatal error: Uncaught Error: Class "Drupal\Core\Entity\Plugin\EntityReferenceSelection\DefaultSelection" not found in /home/www/drupal8/test/core/modules/user/src/Plugin/EntityReferenceSelection/UserSelection.php:27 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/user/src/Plugin/EntityReferenceSelection/UserSelection.php on line 27