private function cacheIssueStats($year)
{
$cache = $this->container->get('file_cache');
$generator = $this->container->get('ojs.graph.data.generator');
$data = ['issuePublish' => $generator->generateIssuePublishCountData($year)];
$cache->save('issue_statistics_' . $year, $data, 1800);
return true;
}