def get_param(self, param, default=None):
        """ Get a parameter in config (handle default value)

        :param param: name of the parameter to recover
        :type param: string
        :param default: the default value, raises an exception
            if param is not in configuration and default
            is None (which is the default value).
        :type default: string or None
        :rtype: the value of the parameter or the default value if
            not set in configuration
        """
        if param in self.config:
            return self.config[param]
        elif default is not None:
            return default
        else:
            raise MissingParameter('ppolicy', param)