Fatal error: Uncaught Error: Class "Drupal\migrate_drupal\Plugin\migrate\FieldMigration" not found in /home/www/drupal8/test/core/modules/comment/src/Plugin/migrate/D7Comment.php:10 Stack trace: #0 {main} thrown in /home/www/drupal8/test/core/modules/comment/src/Plugin/migrate/D7Comment.php on line 10