def METHOD_NAME(cls, filename: Union[os.PathLike, str]):
    """Load the default configuration."""
    new = cls()
    mapping = _read_config_file(filename)
    # Add defaults that are not available in esmvalcore/config-user.yml
    mapping['check_level'] = CheckLevels.DEFAULT
    mapping['config_file'] = filename
    mapping['diagnostics'] = None
    mapping['extra_facets_dir'] = tuple()
    mapping['max_datasets'] = None
    mapping['max_years'] = None
    mapping['resume_from'] = []
    mapping['run_diagnostic'] = True
    mapping['skip_nonexistent'] = False
    new.update(mapping)
    return new