TreeView throws IllegalArgumentException when presenting an empty graph

[benzht]

When you try to present an empty tree view, prefuse complains:

Jul 17, 2013 2:16:03 PM prefuse.action.ActionList run
WARNING: Invalid row index: 0
java.lang.IllegalArgumentException: Invalid row index: 0
at prefuse.data.tuple.TupleManager.getTuple(Unknown Source)
at prefuse.data.tuple.TupleManager$TupleManagerIterator.next(Unknown Source)
at prefuse.data.Graph.getSpanningTree(Unknown Source)
at prefuse.action.filter.FisheyeTreeFilter.run(Unknown Source)
at prefuse.action.ActionList.run(Unknown Source)
at prefuse.action.Action.run(Unknown Source)
at prefuse.activity.Activity.runActivity(Unknown Source)
at prefuse.activity.ActivityManager.run(Unknown Source)

To reproduce modify Prefuse/demos/prefuse/demos/TreeView#setUpData(), comment all lines after the creation of the graph, and start it.