Fatal error: Uncaught Error: Class "Drupal\Core\Form\FormBase" not found in /home/www/drupal8/test/core/modules/config/src/Form/ConfigExportForm.php:13
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/modules/config/src/Form/ConfigExportForm.php on line 13