Fatal error: Uncaught Error: Class "Drupal\Core\Form\ConfirmFormBase" not found in /home/qcsvlel/www/core/modules/workspaces/src/Form/WorkspaceMergeForm.php:20 Stack trace: #0 {main} thrown in /home/qcsvlel/www/core/modules/workspaces/src/Form/WorkspaceMergeForm.php on line 20