presto-main/src/main/java/io/prestosql/sql/planner/iterative/rule/PushAggregationThroughOuterJoin.java/PushAggregationThroughOuterJoin/getSymbolMapping
class PushAggregationThroughOuterJoin:        public Map<Symbol, Symbol> getSymbolMapping()
        {
            return symbolMapping;
        }