Even with non-compulsory voting, you can sometimes find elections with "Re-Open Nominations" (or RON) as a valid option. It doesn't exist in our system because I guess no-one saw the need for it. Either not turning up, or spoiling a ballot, would do. Also, I suppose, Re-Opening nominations in a student union election is just a matter of wasting two or three kids' time for another week, whereas in a General Election it could potentially force a by-election or two and slow the entire process of running the country down.