iOS15 Can't execute Sound only Local Notification.

Hello All. iOS15 can't play sound sound only Local Notification.

Before iOS15 I can use following code.title, body and subtitle is @"" (No charactor).

UNMutableNotificationContent* content = [[UNMutableNotificationContent alloc] init];

  content.title = @"";
  content.body = @"";
  content.subtitle = @"";
  content.sound = [UNNotificationSound soundNamed:@"test"];

When iOS15, I need add content.title for play sound. I don't want display Notification on banner and notification center also Lock Screen.

I want use Sound only Local Notification. Is it a specification of iOS15 or BUGS?