Orchestrator, use of XML object as attributes

Hello

I want to use xml objects as attribute on workflows to create actions for adding a node for example

for this I need to create  parameters of type void or xmlnode according to the documentation

http://www.vroapi.com/Class/XML/5.5.1/XMLDocument

vRO API Explorer by Dr Ruurd and Flores of ITQ

but in configuring attribute on workflow xmlnode and void types does not exist

I have tried any type

but when loading the xml to an attribute

XMLDocument = XMLManager.loadDocument(XMLin,false);

it gives me an error 

[2017-03-13 12:16:39.207] [I] Cannot create XMLDocument object : java.lang.NullPointerException

is the only solution  to pass string values ? and to have to reload all the objects in each modules of the workflow?