def assert_empty(self, class_name: str):
        """
        Raises a ``ConfigurationError`` if ``self.params`` is not empty.  We take ``class_name`` as
        an argument so that the error message gives some idea of where an error happened, if there
        was one.  ``class_name`` should be the name of the `calling` class, the one that got extra
        parameters (if there are any).
        """
        if self.params:
            raise ConfigurationError("Extra parameters passed to {}: {}".format(class_name, self.params))