code: @GwtIncompatible("java.io.ByteArrayOutputStream")
    public byte[] toBytes() {
      ByteArrayOutputStream baos = new ByteArrayOutputStream();
      Writer writer = new OutputStreamWriter(baos, UTF_8);
      try {
        // The output order should be stable.
        for (Map.Entry<String, String> entry :
            ImmutableSortedSet.copyOf(comparingByKey(), map.entrySet())) {
          writer.write(escape(entry.getKey()));
          writer.write(SEPARATOR);
          writer.write(escape(entry.getValue()));
          writer.write('\n');
        }
        writer.close();
      } catch (IOException e) {
        // Note: A ByteArrayOutputStream never throws IOException. This try/catch
        // is just here to appease the Java compiler.
        throw new RuntimeException(e);
      }
      return baos.toByteArray();
    }
docs: Serializes the variable map to a byte array.