Is there any reason why System.Object cannot be selected in the PreferedTypes editor? Did you think its not needed or that maybe its a bad idea to include it there?
(I need to pass a List<System.Object> to a node to avoid too much of a code change elsewhere in my project)
Actually, never mind, i can just wrap the List<Object> in another type and pass that to a node instead that is in Prefered Types list and no need then for any change!