We went over this one a long time ago, Aidan. ;) Vanilla doesn't return nulls and you shouldn't either:

https://github.com/CoFH/Feedback/issues/339

Uh oh, I thought I changed all those. What machine was the Itemduct connected to?

Seems to be a logistical sorter:
https://gist.github.com/Brycey92/8796fe3139d2499b7f32

Alright then :) Awesome. I'll shut it down.

BTW, a good way to handle this is to just have a static ItemStack[] NO_SLOTS = new ItemStack {}; in your code somewhere and just refer to it whenever you need to.

I do exactly that, actually.
Tell them to update Mekanism, they're using v7 :)