public function nextPage(Page $previousPage = null)
    {
        if (is_null($previousPage)) {
            $this->startIndex = $this->startIndex + $this->pageSize;
            return $this;
        }

        if (!($previousPage instanceof AdGroupBidLandscapePage) &&
            !($previousPage instanceof CriterionBidLandscapePage)) {
            throw new InvalidArgumentException('The page object must be an' .
                ' instance of either `AdGroupBidLandscapePage` or' .
                ' `CriterionBidLandscapePage` type');
        }

        $this->startIndex = $this->startIndex +
            self::countLandscapePoints($previousPage);

        return $this;
    }