presto-spi/src/main/java/io/prestosql/spi/type/MapType.java/MapType/createBlockFromKeyValue
class MapType:    public Block createBlockFromKeyValue(Optional<boolean[]> mapIsNull, int[] offsets, Block keyBlock, Block valueBlock)
    {
        return MapBlock.fromKeyValueBlock(
                mapIsNull,
                offsets,
                keyBlock,
                valueBlock,
                this);
    }