PHP Fatal error: Uncaught Error: Call to a member function getReviewerId() ...ReviewerHandler.inc.php:80

Hi,
A reviewer received the invitation to review an article in the email but when a reviewer clicks on the link provided in the email, it through HTTP Error 500.
The PHP error log shows the following:

[26-May-2020 14:59:01 UTC] PHP Deprecated: Non-static method AccessKeyManager::generateKeyHash() should not be called statically in /home/seisense/journal.seisense.com/pages/reviewer/ReviewerHandler.inc.php on line 77
[26-May-2020 14:59:01 UTC] PHP Fatal error: Uncaught Error: Call to a member function getReviewerId() on null in /home/seisense/journal.seisense.com/pages/reviewer/ReviewerHandler.inc.php:80
Stack trace:
#0 /home/seisense/journal.seisense.com/pages/reviewer/ReviewerHandler.inc.php(38): ReviewerHandler->_validateAccessKey(Object(Request))
#1 /home/seisense/journal.seisense.com/lib/pkp/classes/core/PKPRouter.inc.php(383): ReviewerHandler->authorize(Object(Request), Array, Array)
#2 /home/seisense/journal.seisense.com/lib/pkp/classes/core/PKPPageRouter.inc.php(231): PKPRouter->_authorizeInitializeAndCallRequest(Array, Object(Request), Array, false)
#3 /home/seisense/journal.seisense.com/lib/pkp/classes/core/Dispatcher.inc.php(143): PKPPageRouter->route(Object(Request))
#4 /home/seisense/journal.seisense.com/lib/pkp/classes/core/PKPApplication.inc.php(278): Dispatcher->dispatch(Object(Request))
#5 /home/seisense/journal.seisense.com/index.php(68): PKPApplication->execute()
#6 {main}
thrown in /home/seisense/journal.seisense.com/pages/reviewer/ReviewerHandler.inc.php on line 80
OJS: 3.2.0.3
Please provide me with a solution.
Thanks