presto-main/src/main/java/io/prestosql/type/UuidType.java/UuidType/appendTo
class UuidType:    @Override
    public void appendTo(Block block, int position, BlockBuilder blockBuilder)
    {
        if (block.isNull(position)) {
            blockBuilder.appendNull();
        }
        else {
            blockBuilder.writeLong(block.getLong(position, 0));
            blockBuilder.writeLong(block.getLong(position, SIZE_OF_LONG));
            blockBuilder.closeEntry();
        }
    }