Unsets specified option and/or section in the config.

        Args:
            config (configobj.ConfigObj): config to work on.
            section (str): section name.
            opt (str): optional option name.

def unset(config, section, opt=None):
        """Unsets specified option and/or section in the config.

        Args:
            config (configobj.ConfigObj): config to work on.
            section (str): section name.
            opt (str): optional option name.
        """
        if section not in config.keys():
            raise ConfigError("section '{}' doesn't exist".format(section))

        if opt is None:
            del config[section]
            return

        if opt not in config[section].keys():
            raise ConfigError(
                "option '{}.{}' doesn't exist".format(section, opt)
            )
        del config[section][opt]

        if not config[section]:
            del config[section]