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