Save the cleaned data to the initial object or creating a new one
        (if a `model_class` was provided).

def save(self, backref_obj=None):
        """Save the cleaned data to the initial object or creating a new one
        (if a `model_class` was provided).
        """
        if not self.validated:
            assert self.is_valid()

        if self._model and not self._obj:
            obj = self._save_new_object(backref_obj)
        else:
            obj = self.save_to(self._obj)

        for key, subform in self._forms.items():
            data = subform.save(obj)
            if self._model and not data:
                continue
            set_obj_value(obj, key, data)

        for key, formset in self._sets.items():
            data = formset.save(obj)
            if self._model and not data:
                continue
            set_obj_value(obj, key, data)
        return obj