Set content_model to the child class's related name, or None if this is
        the base class.

def set_content_model(self):
        """
        Set content_model to the child class's related name, or None if this is
        the base class.
        """
        if not self.content_model:
            is_base_class = (
                base_concrete_model(ContentTyped, self) == self.__class__)
            self.content_model = (
                None if is_base_class else self.get_content_model_name())