Fatal error: Uncaught Error: Class "Drupal\Core\Form\FormBase" not found in /home/qcsvlel/www/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeFormBase.php:17 Stack trace: #0 {main} thrown in /home/qcsvlel/www/core/modules/migrate_drupal_ui/src/Form/MigrateUpgradeFormBase.php on line 17