How to use the dowhy.causal_refuters.get_class_object function in dowhy

"""Refute an estimated causal effect.

        If method_name is provided, uses the provided method. In the future, we may support automatic selection of suitable refutation tests.

        :param estimand: target estimand, an instance of the IdentifiedEstimand class (typically, the output of identify_effect)
        :param estimate: estimate to be refuted, an instance of the CausalEstimate class (typically, the output of estimate_effect)
        :param method_name: name of the refutation method
        :param **kwargs:  (optional) additional method-specific arguments that are passed directly to the refutation method

        :returns: an instance of the RefuteResult class

        """
        if method_name is None:
            pass
        else:
            refuter_class = causal_refuters.get_class_object(method_name)

        refuter = refuter_class(
            self._data,
            identified_estimand=estimand,
            estimate=estimate,
            **kwargs
        )
        res = refuter.refute_estimate()
        return res