Fatal error: Uncaught Error: Class 'Drupal\Core\Plugin\DefaultPluginManager' not found in /var/www/html/tmp/contrib/flag/src/FlagType/FlagTypePluginManager.php:12 Stack trace: #0 {main} thrown in /var/www/html/tmp/contrib/flag/src/FlagType/FlagTypePluginManager.php on line 12