User test exposed a non-exhaustive match case in Infoset.scala. Added a default case that returns 'null'. Added a check to the InteractiveDebugger's getInfoset method to check for 'null' before attempting to find the root node.
Issue was reproduced and verified corrected
via a separate Java project in Eclipse.
Adds a simpler version of the user
submitted test that exposed the match
Changes "display info infoset" to
"display eval node .." to ease the
verbosity of the trace.