I would say why not do the get current document within python instead. There are some examples of this with the filterelementcollector that should help to guide you on understanding things.
dynamoPython/revitAPI at master · Amoursol/dynamoPython
I will add that there has been previous issues which includes this one and is one reason not to add current document via dynamo node and to do it within python - Python Error: Expected Document, Got Document - Developers - Dynamo