First off let me say that I'm not sure this is a bug in mason or a problem 
with my implementation.  Basically I have agents that exist in 3d space 
and in a network (visualized by SpatialNetwork3D). Each of these agents 
has the ability to create/destroy links to other agents in the network as 
the simulation progresses.  My problem is two-fold (though I expect they 
are very much related).  

First -
When the simulation is running, the network object is being updated 
correctly however the edges that are being visualized seem to only be 
edges which were present when the simulation began (some type of edge 
portrayal update problem?).

Second - 
After some time running the simulation for a given (not consistent) number 
of generations I recieve this error

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
 at sim.portrayal3d.FieldPortrayal3D.getModel
 at sim.display3d.Display3D.updateSceneGraph(
 at sim.display3d.Display3D$
 at java.awt.event.InvocationEvent.dispatch(Unknown Source)
 at java.awt.EventQueue.dispatchEvent(Unknown Source)
 at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown 
 at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
 at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown 
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
 at Source)

I'm not able to attach source code, but I will provide as much requested  
additional information that I can. 

Thanks so much for your help,

Jesse St. Charles
Oak Ridge National Laboratory
Applied Software Engineering Research Group