presto-spi/src/main/java/io/prestosql/spi/block/MapHashTables.java/MapHashTables/MapHashTables
class MapHashTables:    MapHashTables(MapType mapType, Optional<int[]> hashTables)
    {
        this.mapType = mapType;
        this.hashTables = hashTables.orElse(null);
    }