Fatal error: Uncaught Error: Class "Drupal\Core\Render\Element\FormElement" not found in /home/www/drupal8/test/core/lib/Drupal/Core/Render/Element/Checkbox.php:26
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/core/lib/Drupal/Core/Render/Element/Checkbox.php on line 26