code: @GwtIncompatible("Unnecessary")
    private Writer fileNameToOutputWriter2(String fileName) throws IOException {
      if (fileName == null) {
        return null;
      }
      if (isInTestMode()) {
        return new StringWriter();
      }
  
      return streamToOutputWriter2(filenameToOutputStream(fileName));
    }
docs: Converts a file name into a Writer taking in account the output charset. Returns null if the
  file name is null.