Fatal error: Uncaught Error: Class "Drupal\migrate_drupal\Plugin\migrate\FieldMigration" not found in /home/www/drupal8/test/core/modules/user/src/Plugin/migrate/User.php:11 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/user/src/Plugin/migrate/User.php on line 11