I used `copyOf` to ensure that `notes` was immutable. If `notes` should be mutable, then I would add a `setNotes` method.

When I wrote this, I thought that `notes` should be immutable because you can't save changed notes back to the server. I suppose, however, that mutable `notes` could be useful for making changes within an application and passing them on; for example, a blacklist might want to strip out some of the notes and pass the post on to the rest of the application.