Merge pull request #62280 from nextcloud/backport/61622/stable33

[stable33] fix(files_external/SMB): Use 'null' explicitly for no workgroup

Author: AndyScherzinger

apps/files_external/lib/Lib/Backend/SMB.php

@@ -69,7 +69,7 @@ public function manipulateStorageConfig(StorageConfig &$storage, ?IUser $user =
 
 			$smbAuth = new BasicAuth(
 				$storage->getBackendOption('user'),
-				$storage->getBackendOption('domain'),
+				$storage->getBackendOption('domain') ?: null,
 				$storage->getBackendOption('password')
 			);
 		} else {