keras/src/metrics/metrics_utils.py/parse_init_thresholds
def parse_init_thresholds(thresholds, default_threshold=0.5):
    if thresholds is not None:
        assert_thresholds_range(to_list(thresholds))
    thresholds = to_list(
        default_threshold if thresholds is None else thresholds
    )
    return thresholds