begin
before A
java.lang.NullPointerException
	at EDU.neu.ccs.demeter.dj.TraversalGraph.shouldTraverse(TraversalGraph.java:291)
	at EDU.neu.ccs.demeter.dj.TraversalGraph.traverse(TraversalGraph.java:102)
	at EDU.neu.ccs.demeter.dj.TraversalGraph.traverse(TraversalGraph.java:52)
	at Main.main(Main.java:21)