code: @GwtIncompatible("Unnecessary")
    private Writer streamToLegacyOutputWriter(OutputStream stream) throws IOException {
      if (legacyOutputCharset == null) {
        return new BufferedWriter(new OutputStreamWriter(stream, UTF_8));
      } else {
        return new BufferedWriter(
            new OutputStreamWriter(stream, legacyOutputCharset));
      }
    }
docs: Create a writer with the legacy output charset.