[Design] What is the sum aggregator for a non-existing value?

[anjakefala]

Kivell has never sold a Pencil.

Previously, his mean_Pencil would be Null, and the sum_Pencil would be 0.

With 1c466d8 now the sum_Pencil is similarly Null.

Which is your preferred behaviour? =)

[maxim-uvarov]

Sum_Pencil = 0 seems to me more logical

[LaPingvino]

I think converting null to 0 is trivial, but the second way to do it adds possible information that you can work with that wouldn't be there otherwise... I think both ways have their merit honestly!