presto-spi/src/main/java/io/prestosql/spi/block/AbstractSingleMapBlock.java/AbstractSingleMapBlock/writePositionTo
class AbstractSingleMapBlock:    @Override
    public void writePositionTo(int position, BlockBuilder blockBuilder)
    {
        position = getAbsolutePosition(position);
        if (position % 2 == 0) {
            getRawKeyBlock().writePositionTo(position / 2, blockBuilder);
        }
        else {
            getRawValueBlock().writePositionTo(position / 2, blockBuilder);
        }
    }