Fatal error: Uncaught Error: Class "Drupal\file\Plugin\migrate\field\d6\FileField" not found in /home/www/drupal8/test/core/modules/file/src/Plugin/migrate/field/d7/FileField.php:16 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/file/src/Plugin/migrate/field/d7/FileField.php on line 16