Actually, for Adelaide University Union elections, there is a No Candidate option on the ballot. The election is run as an ordinary preferential ballot, except if No Candidate wins an absolute majority then the position is left vacant.
They also have Council Vacant for ballots where multiple vacancies are to be filled. These are filled using Hare-Clark proportional representation, except if Council Vacant wins more than half first preference votes then all positions are vacant.
I would like to see them do something like this in parliamentary elections. I suppose if that were tried, though, and three parties were equally strong and equally opposed, there would be a lot of half-empty parliaments.