presto-main/src/main/java/io/prestosql/util/GraphvizPrinter.java/NodePrinter/visitPlan
class NodePrinter:        @Override
        protected Void visitPlan(PlanNode node, Void context)
        {
            throw new UnsupportedOperationException(format("Node %s does not have a Graphviz visitor", node.getClass().getName()));
        }