@property
    @memoized
    def start_date(self):
        if not self.start_date_str:
            return None

        try:
            return iso_string_to_datetime(self.start_date_str)
        except (__HOLE__, ValueError):
            return None
dataset/ETHPy150Open dimagi/commcare-hq/corehq/apps/sms/views.py/ChatMessageHistory.start_date