code: public String getOptionValue(char opt, String defaultValue)
      {
          return getOptionValue(String.valueOf(opt), defaultValue);
      }
docs: Retrieve the argument, if any, of an option.
  
  @param opt character name of the option
  @param defaultValue is the default value to be returned if the option
  is not specified
  @return Value of the argument if option is set, and has an argument,
  otherwise <code>defaultValue</code>.