Australia has compulsory voting.
Spoiling or failing to mark a ballot correctly is a crime.
Australian ballot papers are single sheets of paper for each constituency being elected. They are to be marked by pencil. I think referreda are all questions on one paper, can't remember.
This crime isn't enforced, and couldn't be due to the secrecy of the election, unless someone does something daft like removing their ballots from the polling place and then posting video evidence that they'd left their paper blank on YouTube.
There are some unusual edge cases where a "below the line" ballot could conceivably run through all
150 12 valid preferences and exhaust without assigning all of its value to one of the last two candidates. (MMP quota preferential voting is weird, but achieves accepted outcomes here). The reason for requiring at least 150 preferences in the past, or at least 12, is that for a half senate election each vote is worth 1/6th of a seat. But that the vote must be counted "fully," ie: be available to be exhausted in the last two candidates vying for the last seat. To work this out you need to work out the "quota," ie, how many votes it takes to fill a seat: (Number of formal ballot papers / (Number of senators to be elected + 1)) rounded down + 1 = Senate quota. The last two candidates will need to make up their quota from transferred fractions of votes which have previously been used to elect others. For example. With a half senate election, and 150000 votes for quota, and 350000 votes for labour, and 350000 votes for liberal, each of the individual votes for labour (after electing two senators) will be worth (350000 - 150000 - 150000) / 350000, or 1/7th of a vote. If you took that 1/7th of a vote away from the 700000 people who voted for labour or liberal with their first preference, you'd be denying them a vote, so each of their individual votes flows to the 3rd preference of those electors. To prevent vote wastage, in the past electors who voted for individual candidates "below the line" had to vote for 150 or so candidates. If your state had fewer than 150, good for you, if you voted in NSW with 250 candidates (six to be returned), you had to number at least 150 candidates. Now you only have to number 12. So the rate of vote wastage has increased. This was largely due to above the line "list-voting" shenanigans with a guy specialising in creating nonsense parties to channel right wing votes from working class fascists, reactionaries and tories who'd vote for the "dog smugglers' party" but not "respectable conservative party, perhaps not far enough right wing despite running concentration camps." As part of the above the line list voting reform, they made voting lawfully below the line easier. You used to only get 3 "errors" allowed in a below the line vote. Everyone knows the system is rigged for the 2.75 party system (climbing towards 2.95) but many people vote below the line to "give electoral workers employment," or to "piss off politicians," or because they don't trust the party they'd vote for's list to not preference loony lefts or fascist running dogs.
The claims at https://magnacarta.moadoph.gov.au/story/albert-langer/ are humourous. "Mark" such as in s. 200DK (a) can clearly be found to have a common law meaning. ss. 233 and 239/240 are clearer still. s. 339 1 (d) has a gaol sentence attached.