Fatal error: Uncaught Error: Class "Drupal\file\Plugin\migrate\process\d6\FieldFile" not found in /home/www/drupal8/test/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php:17 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/file/src/Plugin/migrate/process/d6/CckFile.php on line 17