presto-rcfile/src/main/java/io/prestosql/rcfile/binary/StringEncoding.java/StringEncoding/encodeColumn
class StringEncoding:    @Override
    public void encodeColumn(Block block, SliceOutput output, EncodeOutput encodeOutput)
    {
        for (int position = 0; position < block.getPositionCount(); position++) {
            if (!block.isNull(position)) {
                Slice slice = type.getSlice(block, position);
                if (slice.length() == 0) {
                    output.writeByte(HIVE_EMPTY_STRING_BYTE);
                }
                else {
                    output.writeBytes(slice);
                }
            }
            encodeOutput.closeEntry();
        }
    }