Multiple user.name and user.email (possible feature request)

Is there a way to have *no* default or some invalid default for the name/email -- something that will make git refuse to create a commit?

For example, I'd be happy if I could put this in my global config:

  [user]
    name = "Eli Barzilay"
    email = "-"

and then have git barf at me when I try to commit with these settings, since I prefer being forced to set the appropriate address for each repository rather than deal with the alternative confusion (or just accepting the limitations and always using the same name/email).

[When I tried to see if it's possible I was surprised to see that git happily creates commits for "- <->" and even " <>".]