def validate_series(df: pd.DataFrame, station: str) -> pd.DataFrame:
    """
    Make sure a series is formatted correctly
    """

    # Add missing column(s)
    if "time" not in df.columns:
        df["time"] = None

    # Add weather station ID
    df["station"] = station

    # Set index
    df = df.set_index(["station", "time"])

    # Return DataFrame
    return df

    Make sure a series is formatted correctly
    
meteostat/utilities/validations.py