the obtained message not necessarily is related to errors of the invoked Web Service. It seems that the document object is returned with a content, but its name property has a null value.
You could try to use the SOAP UI software, that allows you to invoke the Web service by providing an appropriate input xml document. In this way you can see the result returned by the Web Service and understand if the Web Service failed or succeeded.
In addition, you could try to print the response document on the console, by using a Script Unit containing the following instruction:
println doc.asXML(); // doc is the xml document received in input