The mod has fission and fusion reactors as personal equipment which need fuel to run, and this apparently causes a problem with obj.get_output_inventory() and obj.request_slot_count which isn't caught by the check if they do exist because simply checking if those exist causes an error.
I'm not exactly sure what i'm doing but i think i fixed it by adding a check
if obj.name ~= "fusion-reactor-equipment" and obj.name ~= "undarl-fission-reactor-equipment"
for both functions for output inventory and request slots which seems to have done the trick. You can probably do that more elegantly by checking if it's a personal equipment type item, but i don't know how to do that and this hack works for me right now :P Setting filters in cargo wagons still works so i'm at least not aware that i broke anything. Link to changed mod: https://www.dropbox.com/s/pchrrnv1hpzbvyz/fast-filter-fill_0.6.4.zip?dl=0
