AKC, AKE, AKH and DPE are all the codes supported right now for ULD containers.
"" it's the same as BELT, which means you want a baggage conveyor belt in any case.
AUTO means "select automatically", using the door height as a threshold, less than 2.10 meters it's a conveyor, more than 2.10 meters, it's an AKH container
I'm not sure if None is still recognized in the current version, because BELT and AUTO are more easy to understand, but if it is, should be the same as as "".