Fatal error: Uncaught Error: Class "Drupal\webform\Plugin\WebformElement\WebformCompositeBase" not found in /home/www/drupal8/test/modules/webform/src/Plugin/WebformElement/WebformCustomComposite.php:21 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/Plugin/WebformElement/WebformCustomComposite.php on line 21