diff --git a/src/Support/NotificationPayloadFactory.php b/src/Support/NotificationPayloadFactory.php
index 9014d02..1e39c75 100644
--- a/src/Support/NotificationPayloadFactory.php
+++ b/src/Support/NotificationPayloadFactory.php
@@ -141,7 +141,7 @@ class NotificationPayloadFactory
 			return (string) $subject->discussion->title;
 		}
 
-		return;
+		return null;
     }
     protected function resolveSubjectUrl(BlueprintInterface $blueprint): ?string
     {