That is one use where either can be used.

However contracts cover a lot of other cases (and as the other replies point out contracts are probably the wrong answer here - a concept is your right answer allow someone else to write a new/different Gonzo complaint widget in the fiture). A contract can check cases where have the right type, but something is wrong anyway. If you need a sorted list a contract can check that....

Likewise exception is useful for a lot of things that should not be a contract. Running out of disk space is still a common problem - you do not want a contract that there is enough disk space, this is an error you need to ask how to handle (often the user would free up disk space external to your program and retry a save).