Fatal error: Uncaught Error: Interface "Drupal\Component\Plugin\PluginManagerInterface" not found in /home/www/drupal8/test/modules/webform/src/Plugin/WebformSourceEntityManagerInterface.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/modules/webform/src/Plugin/WebformSourceEntityManagerInterface.php on line 10