Error for historical DWD import

[FWuellhorst]

Describe the bug Loading data with the following script for Tempelhof Berlin historical data, I get values -999 for temperatures not recognized as NAN and IndexErrors.

To Reproduce Steps to reproduce the behavior in current dev.

    # initiate the project class which contains or creates all variables and functions
    for year in [
        2019,
        2022,
        2023
    ]:
        DWD_pull_project = ProjectClassDWDHistorical(
            start=dt.datetime(year, 1, 1),
            end=dt.datetime(year + 1, 1, 1),
            station=433,  # Dahlem
            # specify whether nan-values should be filled when exporting
            fillna=True,
            # define results path if desired
            abs_result_folder_path=None,
        )
        # import historical weather from the DWD open access database
        DWD_pull_project.import_data()

Expected behavior No errors.