def ts_inverse_transform(
            series: TimeSeries, params: Mapping[str, Any], **kwargs
        ) -> TimeSeries:
            """
            Implements the inverse transform `series + mean`.
            """
            mean = params["fitted"]
            vals = series.all_values()
            vals += mean
            return series.from_values(vals)

            Implements the inverse transform `series + mean`.
            
darts/tests/dataprocessing/transformers/test_invertible_fittable_data_transformer.py