[RhinoCommon] UserData must be defined in a plug-in assembly - NullReferenceException otherwise

I have a plug-in that loads a file resulting in a Mesh. To this I want to add a UserData definition. I have found that when the class definition of the UserData is not in a plug-in assembly, that I get a NullReferenceException:

   at Rhino.DocObjects.Custom.UserData.NonConstPointer(Boolean createIfMissing)
   at Rhino.DocObjects.Custom.UserDataList.Add(UserData userdata)
<snip my code>

It would be nice if this restriction could be lifted somehow.

Yep, I don’t know quite how I would do this, but the bug is in the system at

Ok, thanks.