Proxy property to smartly access the classes from the estimator or
        stored locally on the score visualizer for visualization.

def classes_(self):
        """
        Proxy property to smartly access the classes from the estimator or
        stored locally on the score visualizer for visualization.
        """
        if self.__classes is None:
            try:
                return self.estimator.classes_
            except AttributeError:
                return None
        return self.__classes