protected function getMinPage()
    {
        $minPageNumber = null;
        $minPage       = null;
        foreach ($this->pages as $page) {
            $pageNumber = $page->getPageNumber();
            if ($minPageNumber === null || $pageNumber < $minPageNumber) {
                $minPageNumber = $pageNumber;
                $minPage       = $page;
            }
        }
        return $minPage;
    }