docs: def clear_option_value(self, opt_name):
          """ Clear the stored option value (so the default will be used)
  
          :param opt_name: option name
          :type opt_name: str
          """
          if not self.has_option(opt_name):
              raise ValueError("Unknow option name (%s)" % opt_name)
          self._options[opt_name].clear()