presto-rcfile/src/main/java/io/prestosql/rcfile/text/BlockEncoding.java/BlockEncoding/encodeColumn
class BlockEncoding:    @Override
    public final void encodeColumn(Block block, SliceOutput output, EncodeOutput encodeOutput)
            throws RcFileCorruptionException
    {
        for (int position = 0; position < block.getPositionCount(); position++) {
            if (block.isNull(position)) {
                output.writeBytes(nullSequence);
            }
            else {
                encodeValueInto(1, block, position, output);
            }
            encodeOutput.closeEntry();
        }
    }