Yield the parameter values, with optional deprecation warning as second tuple value.

        The parameter value will be whatever non-_no_value that is yielded first.

def _value_iterator(self, task_name, param_name):
        """
        Yield the parameter values, with optional deprecation warning as second tuple value.

        The parameter value will be whatever non-_no_value that is yielded first.
        """
        cp_parser = CmdlineParser.get_instance()
        if cp_parser:
            dest = self._parser_global_dest(param_name, task_name)
            found = getattr(cp_parser.known_args, dest, None)
            yield (self._parse_or_no_value(found), None)
        yield (self._get_value_from_config(task_name, param_name), None)
        if self._config_path:
            yield (self._get_value_from_config(self._config_path['section'], self._config_path['name']),
                   'The use of the configuration [{}] {} is deprecated. Please use [{}] {}'.format(
                       self._config_path['section'], self._config_path['name'], task_name, param_name))
        yield (self._default, None)