Fatal error: Uncaught Error: Class "Drupal\search\Form\SearchPageFormBase" not found in /home/www/drupal8/test/core/modules/search/src/Form/SearchPageAddForm.php:12 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/search/src/Form/SearchPageAddForm.php on line 12