I get this error when attempting to place any entity:
Error while running the event handler: autofill/control.lua:49: attempt to index field '?' (a nil value)

This is with Autofill 1.41 on Factorio version 0.13.11

This is the first chance I've had to start poking at 0.13 and I'm still in the process of checking compatibility of our previous mod set. The error does not happen on a new map start. It does happen when I attempt to load a prior save from 0.12.35 (it's a multiplayer save being loaded in single player, if that matters).

Sorry for the delay, I don't get noticed when someone posts here.
I think I know what is going on in the meantime..
Can you check your settings before you load the world and let me know if your username field is blank? and if it is can you set it to something and try loading your game.

If neither of those work try /c remote.call("af","resetMod",true)

Should be temporarily fixed in 1.4.2
https://github.com/Nexela/autofill/issues/2