public function toRegionTimeZone(DateTimeInterface $date = null)
    {
        $tz = $this->toRegionName($date);

        if ($tz === false) {
            if (Carbon::isStrictModeEnabled()) {
                throw new InvalidArgumentException('Unknown timezone for offset '.$this->getOffset($date ?: Carbon::now($this)).' seconds.');
            }

            return false;
        }

        return new static($tz);
    }