Configure a temporary state containing an object with a null value:
Configure a transformer that accesses that value:
Note that if you hover over the value in the transformer, it is correctly displayed as null:
The return value of the transformer is undefined:
I have also tested this with other resources that are not temporary states. For example, if accessing a null value directly from a resource query backed by Postgres, this does not happen. It seems to be isolated just to temporary states.