diff --git a/apps/theming/lib/Controller/ThemingController.php b/apps/theming/lib/Controller/ThemingController.php
index 6d4bd4bae60..aca7fafa76e 100644
--- a/apps/theming/lib/Controller/ThemingController.php
+++ b/apps/theming/lib/Controller/ThemingController.php
@@ -386,7 +386,7 @@ class ThemingController extends Controller {
 			} else {
 				$startUrl = $this->urlGenerator->getBaseUrl() . '/apps/' . $app . '/';
 			}
-			$description = $info['summary'];
+			$description = $info['summary'] ?? '';
 		}
 		$responseJS = [
 			'name' => $name,