Fatal error: Uncaught Error: Class "Drupal\webform\Plugin\WebformElementBase" not found in /home/www/drupal8/test/modules/webform/src/Plugin/WebformElement/WebformHorizontalRule.php:22
Stack trace:
#0 {main}
thrown in /home/www/drupal8/test/modules/webform/src/Plugin/WebformElement/WebformHorizontalRule.php on line 22