[OJS 3.1] Fatal error: Call to a member function getId()

Greetings,

Today I noticed a lot of fatal errors in my error_log but I have not yet noticed any problem with the website. Should I worry or just ignore it?

PHP Fatal error:  Uncaught Error: Call to a member function getId() on null in /home/jlmcedun/public_html/lib/pkp/classes/notification/PKPNotificationManager.inc.php:150
Stack trace:
#0 /home/jlmcedun/public_html/classes/notification/NotificationManager.inc.php(80): PKPNotificationManager->getNotificationMessage(Object(Request), Object(Notification))
#1 /home/jlmcedun/public_html/lib/pkp/classes/notification/PKPNotificationOperationManager.inc.php(53): NotificationManager->getNotificationMessage(Object(Request), Object(Notification))
#2 /home/jlmcedun/public_html/lib/pkp/classes/notification/PKPNotificationManager.inc.php(181): PKPNotificationOperationManager->getNotificationContents(Object(Request), Object(Notification))
#3 /home/jlmcedun/public_html/lib/pkp/classes/notification/PKPNotificationOperationManager.inc.php(427): PKPNotificationManager->getNotificationContents(Object(Request), Object(Notification))
#4 /home/jlmcedun/public_html/lib/pkp/classes/notification/PKPNotificationOperationManager.inc.php(400): PKPNotificati in /home/jlmcedun/public_html/lib/pkp/classes/notification/PKPNotificationManager.inc.php on line 150

Regards,