Fatal error: Uncaught TypeError: array_keys(): Argument #1 ($array) must be of type array, null given in /home/papersdb/web_docs/includes/pdPublication.php:1252 Stack trace: #0 /home/papersdb/web_docs/includes/pdPublication.php(1252): array_keys() #1 /home/papersdb/web_docs/includes/pdPublication.php(958): pdPublication->getInfoForCitation() #2 /home/papersdb/web_docs/view_publication.php(159): pdPublication->getCitationHtml() #3 /home/papersdb/web_docs/view_publication.php(87): view_publication->showPublication() #4 /home/papersdb/web_docs/view_publication.php(264): view_publication->__construct() #5 {main} thrown in /home/papersdb/web_docs/includes/pdPublication.php on line 1252