code: @GwtIncompatible("Unnecessary")
    private Charset getLegacyOutputCharset() {
      if (!config.charset.isEmpty()) {
        if (!Charset.isSupported(config.charset)) {
          throw new FlagUsageException(config.charset + " is not a valid charset name.");
        }
        return Charset.forName(config.charset);
      }
      return US_ASCII;
    }
docs: Query the flag for the output charset.
  
  <p>Let the outputCharset be the same as the input charset... except if we're reading in UTF-8
  by default. By tradition, we've always output ASCII to avoid various hiccups with different
  browsers, proxies and firewalls.
  
  @return Name of the charset to use when writing outputs. Guaranteed to be a supported charset.
  @throws FlagUsageException if flag is not a valid Charset name.