Fatal error: Uncaught Error: Class "Drupal\Core\Database\Query\SelectExtender" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Database/Query/PagerSelectExtender.php:17 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Database/Query/PagerSelectExtender.php on line 17