presto-main/src/main/java/io/prestosql/operator/aggregation/multimapagg/MultimapAggregationStateFactory.java/MultimapAggregationStateFactory/getGroupedStateClass
class MultimapAggregationStateFactory:    @Override
    public Class<? extends MultimapAggregationState> getGroupedStateClass()
    {
        switch (implementation) {
            case NEW:
                return GroupedMultimapAggregationState.class;
            case LEGACY:
                return LegacyGroupedMultimapAggregationState.class;
            default:
                throw new PrestoException(FUNCTION_IMPLEMENTATION_ERROR, format("Unexpected group enum type %s", implementation));
        }
    }