In T316442#8191648, @Emufarmers wrote:

In T316442#8191646, @Base wrote:

have it warn you and ask for confirmation if you try to submit a blank ballot, perhaps requiring you to fill a checkbox to make sure.

Some people might just click through because of a habit to just click ok on any confirmations or because they don't understand what is written if they use an interface language for which Secure Poll isn't translated yet.

Yes, any time we introduce a new capability, we are also introducing a certain amount of unavoidable risk of user error. For STV elections, this risk is probably dwarfed by the risk that people will rank their candidates backwards (which appears to have occurred in the 2019 ASBS process), but we should certainly design the interface to verify to the greatest extent possible that the voter is doing this consciously.

Further mitigation for this and for voting errors in general could come from having your vote displayed to you and/or emailed to you after you vote--but that's another task (T22023; cf. T20969).