def METHOD_NAME(self, config, fields_spec):
    """
    Check that `config` has each field in `fields_spec` if a default
    has not been provided.
    """
    for field, type_info in fields_spec.items():
        has_default = not isinstance(type_info, type)
        if field not in config and not has_default:
            raise RuntimeError(
                "Configuration not complete. %s missing" % field)