@staticmethod
def verify_config_file(config):
    """
        Make sure no values of required parameters are missing from the config file

        Args:
            config (dict): The config dictionary containing the key value pairs pulled from the config file
        Returns:
            Raises ValueError if an empty value is found, None otherwise
        """
    for key in ['galaxy_url', 'galaxy_key', 'history_name',
        'workflow_source', 'workflow']:
        if config[key] is None:
            return key
    return None
