def _generate_new_dates(
    n: int, input_series: TimeSeries, start: Optional[Union[pd.Timestamp, int]] = None
) -> Union[pd.DatetimeIndex, pd.RangeIndex]:
    """
    Generates `n` new dates after the end of the specified series
    """
    if start is None:
        last = input_series.end_time()
        start = last + input_series.freq
    return generate_index(
        start=start, freq=input_series.freq, length=n, name=input_series.time_dim
    )

    Generates `n` new dates after the end of the specified series
    
darts/utils/timeseries_generation.py