Thanks for the good feedback everyone and apologies for the unresponsiveness over the past day.

I understand that my use cases may not reflect wider usage patterns and am not looking to argue against the closing. But anyway, for future reference, I'll add two real-life usage examples, which I should have included originally (again, apologies for the delay, things have been hectic).

The context is that I'm involved in running a coding bootcamp, and these are two recent cases when I needed a default of zero recently:

1. (Separately of the final grade calculations) We are interested in students' average grades on their projects as an indicator of their skills gained and their striving for excellence. When calculating this indicator, we use an average of 0 for a student who haven't yet submitted anything.

2. When providing tutoring support, we classify the "complexity" of each student issue, and then one of our indicators involves the average complexity of questions in a particular slice of time and the programme (this is particularly interesting around changes to the content). For this as well, a slice of time/programme/tutor during which there were no issues would be considered as having a complexity of 0.

Again, not disputing the decision to close, just adding these examples for future reference.
Thanks