presto-main/src/main/java/io/prestosql/operator/aggregation/multimapagg/MultimapAggregationStateFactory.java/MultimapAggregationStateFactory/getSingleStateClass
class MultimapAggregationStateFactory:    @Override
    public Class<? extends MultimapAggregationState> getSingleStateClass()
    {
        return SingleMultimapAggregationState.class;
    }