presto-main/src/main/java/io/prestosql/sql/planner/optimizations/IndexJoinOptimizer.java/IndexKeyTracer/visitPlan
class IndexKeyTracer:            @Override
            protected Map<Symbol, Symbol> visitPlan(PlanNode node, Set<Symbol> lookupSymbols)
            {
                throw new UnsupportedOperationException("Node not expected to be part of Index pipeline: " + node);
            }