[steveklabnik]

You're correct, except that "else" is a keyword and so cannot be used there. You'd want

  _ => None,

instead, which is the "catch all" arm.

(For those that didn't catch it, the parent code is trying to use None, but it's actually a tuple, and there's four different cases here, not two. So the catch-all arm is better than spelling each of them out in this case.)