def METHOD_NAME(date_string: str) -> Union[datetime, None]:
    """Convert a string to a datetime object or None if no string was provided.
    This assumes the date is in the following format: 2023-12-25 (yyyy-mm-dd)
    Args:
        date_string (str): `Earliest Public Law Enactment Date` value from def_codes.csv file
    Returns:
        Union[datetime, None]: Return the `Earliest Public Law Enactment Date` converted to a datetime
            or None
    """
    if date_string and type(date_string) is str:
        return datetime.strptime(date_string, "%Y-%m-%d")
    else:
        return None