public StateFilteringVisitor(final DiffNode.State state) {
   Assert.notNull(state, "state");
   this.state = state;
 }
 public void matchCircularReferencesUsing(
     final CircularReferenceMatchingMode circularReferenceMatchingMode) {
   Assert.notNull(circularReferenceMatchingMode, "circularReferenceMatchingMode");
   this.circularReferenceMatchingMode = circularReferenceMatchingMode;
 }