I think I would like to see a usecase where subs is an array of zero dimension. As I see it this can only happen if you plug in a single number in the instantiation, which is not allowed according to the documentation.

Thank you for pointing me to the documentation. I used a single number in the instantiation and thought this was allowed.

I see. Of course you are free to then change the documentation as well, if you feel like single numbers should be allowed for. Or, if you think that other users may fall for this as well, to provide a better error message in that case.

I made PR #12860 which adds some more explanatory error messages.