If the date is custom, return the end datetime with the format %Y-%m-%d %H:%M:%S. Else, returns "".

def get_std_end_date(self):
        """ If the date is custom, return the end datetime with the format %Y-%m-%d %H:%M:%S. Else, returns "". """
        _, second = self._val
        if second != datetime.max:
            return second.strftime("%Y-%m-%d %H:%M:%S")
        else:
            return ""