:param utc_now: optional parameter to be used by Unit Tests as a definition of "now"
            :return: timedelta instance presenting amount of time before the trigger is triggered next time
         or None if the RepeatTimer instance is not running

def next_run_in(self, utc_now=None):
        """ :param utc_now: optional parameter to be used by Unit Tests as a definition of "now"
            :return: timedelta instance presenting amount of time before the trigger is triggered next time
         or None if the RepeatTimer instance is not running """
        if utc_now is None:
            utc_now = datetime.utcnow()

        if self.is_alive():
            next_run = timedelta(seconds=self.interval_current) + self.activation_dt
            return next_run - utc_now
        else:
            return None