Hi Daniel,
According to the stacktrace attribute Documenttype is empty:
Caused by: com.mendix.systemwideinterfaces.MendixRuntimeException: Exporting an empty object is not allowed when element is neither optional nor nillable (urn:sap-com:document:sap:soap:functions:mc-style:ZDockumentChange03|Documentdata|Documenttype attribute: MyFirstModule.DocDraw2.Documenttype)
Perhaps this will help you find the issue.
Cheers,
Jeffrey