Fatal error: Uncaught Error: Class "Drupal\search\Plugin\SearchPluginBase" not found in /home/www/drupal8/test/core/modules/user/src/Plugin/Search/UserSearch.php:22 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/user/src/Plugin/Search/UserSearch.php on line 22