presto-rcfile/src/main/java/io/prestosql/rcfile/text/BinaryEncoding.java/BinaryEncoding/encodeColumn
class BinaryEncoding:    @Override
    public void encodeColumn(Block block, SliceOutput output, EncodeOutput encodeOutput)
    {
        for (int position = 0; position < block.getPositionCount(); position++) {
            if (block.isNull(position)) {
                output.writeBytes(nullSequence);
            }
            else {
                Slice slice = type.getSlice(block, position);
                byte[] data = slice.getBytes();
                slice = Slices.wrappedBuffer(base64Encoder.encode(data));
                output.writeBytes(slice);
            }
            encodeOutput.closeEntry();
        }
    }