diff --git a/apps/files_sharing/lib/Notification/Notifier.php b/apps/files_sharing/lib/Notification/Notifier.php
index 2499896653b0d..22cf83b547737 100644
--- a/apps/files_sharing/lib/Notification/Notifier.php
+++ b/apps/files_sharing/lib/Notification/Notifier.php
@@ -193,7 +193,7 @@ protected function parseShareInvitation(IShare $share, INotification $notificati
 				}
 
 				$group = $this->groupManager->get($share->getSharedWith());
-				if (!$group->inGroup($user)) {
+				if ($group === null || !$group->inGroup($user)) {
 					throw new AlreadyProcessedException();
 				}