Regarding XML Document on webmethods ID

I’m using WebMethods IS Version 4.6. I’m held up with the following problem.

I’ve created a java service, which creates an XML Document object(org.w3c.dom.Document). I’m not able to place this
object onto the pipeline. Hence I had to put a NodeList object onto the pipeline, which I could.

After that, I wanted to retrieve that NodeList object from the pipeline, using a java service. The system is returning null.
I wanted to know, whether I can put/get any other Document types(other than com.wm.lang.xml.*, I mean the webmethods
defined Document or NodeList object) onto/from the pipeline.