Scheduled Conferences 500

Software Support
1

OCS Version 2.3.5.0
Hello, please help solve the problem. When I try to create another conference, I get a 500 error
https://mysite.com/index.php/ConfName/index/manager
GENERAL MANAGEMENT:
[Scheduled Conferences] and [Prepared Emails] got 500 error.

[26-Jan-2021 12:11:10 UTC] PHP Fatal error: Call to undefined function session_is_registered() in /public_html/conf/lib/pkp/classes/session/Session.inc.php on line 64

2

If I delete :
}

	if (session_is_registered($key)) {
		session_unregister($key);

It looks like it works, am I acting correctly?