There's nothing that says you can't have system messages as a boilerplate part of response bodies, even if you don't populate it. In fact, it's the recommended

There's nothing that says you can't have system messages as a boilerplate part of response bodies, even if you don't populate it. In fact, it's the recommended way to do things like tell a client things it might need to know. Example: "The game servers will be shutting down in 15 minutes for maintenance."