Fatal error: Uncaught Error: Call to a member function getJournalId() on null in /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/classes/issue/IssueAction.inc.php:31 Stack trace: #0 /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/classes/search/ArticleSearch.inc.php(273): IssueAction->subscriptionRequired(NULL, Object(Journal)) #1 /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/plugins/generic/recommendByAuthor/RecommendByAuthorPlugin.inc.php(142): ArticleSearch->formatResults(Array) #2 /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/lib/pkp/classes/plugins/HookRegistry.inc.php(107): RecommendByAuthorPlugin->callbackTemplateArticlePageFooter('Templates::Arti...', Array) #3 /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/lib/pkp/classes/template/PKPTemplateManager.inc.php(1581): HookRegistry::call('Templates::Arti...', Array) #4 /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/cache/t_compile/a4fc84a2d9d2a85c011fcc528 in /home/u412479426/domains/penerbit.org/public_html/jayapanguspress/classes/issue/IssueAction.inc.php on line 31