Here are the simple steps:
1. Create a project and set yourself as the only member.
2. Add a new repository and set its access to members of that project (so just you).
3. Make some changes and create a revision. Add any reviewer to it.
This will succeed. The reviewer will receive an email and a notification about the pending review, but will not be able to navigate to it.
It would be neat if I could get a heads up when I about to do something this silly so I get a chance to fix it.