from typing import List
from typing import Optional


def _normalize_card_expiration(expiration_date: str) -> List[Optional[int]]:
    """Convert authorize.net combined expiration date into month and year.

    Example: 2021-02 > [2021, 2]
    Always return List of length 2
    """
    dates = expiration_date.split("-")
    if len(dates) == 2:
        try:
            return [int(dates[0]), int(dates[1])]
        except ValueError:
            pass
    return [None, None]