Yeah, if it's "multiSource" then you get a List<T> of results. The postProcess is for if there's one result (of type T) to transform it into V. The multiPostProcess is for transforming `<List<T>>` into a `V`. But if one combines a postProcess T->V for each source then the multiPostProcess ends up being `List<V> -> V2`. Not sure if we really support that just now, but generics get really hard trying to say exactly what the inbound type will be for that field!