code: @GwtIncompatible("Unnecessary")
    private Charset getInputCharset() {
      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 UTF_8;
    }
docs: Query the flag for the input charset, and return a Charset object representing the selection.
  
  @return Charset to use when reading inputs
  @throws FlagUsageException if flag is not a valid Charset name.