PHP Warning: Trying to access array offset on value of type null

Hey, I’m trying to add Form Items in Review Forms but every time I press create new Item it generates the following error:
Failed Ajax request or invalid JSON returned.

image

and in the error log:
[Mon Aug 30 11:52:45.143422 2021] [php:warn] [pid 5691] [client 82.137.200.44:47216] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:00.416824 2021] [php:warn] [pid 5690] [client 82.137.200.44:53630] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:00.837439 2021] [php:warn] [pid 5690] [client 82.137.200.44:53630] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:00.844340 2021] [php:warn] [pid 5686] [client 82.137.200.44:53714] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:00.850553 2021] [php:warn] [pid 5735] [client 82.137.200.44:53894] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:26.116212 2021] [php:warn] [pid 5691] [client 82.137.200.44:24313] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:26.155466 2021] [php:warn] [pid 5691] [client 82.137.200.44:24313] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:26.695111 2021] [php:warn] [pid 5688] [client 82.137.200.44:34536] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:26.703686 2021] [php:warn] [pid 5691] [client 82.137.200.44:24313] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:53:41.733044 2021] [php:warn] [pid 6892] [client 82.137.200.44:26856] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:54:11.753263 2021] [php:warn] [pid 6894] [client 82.137.200.44:62423] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة
[Mon Aug 30 11:54:12.885376 2021] [php:warn] [pid 6894] [client 82.137.200.44:62423] PHP Warning: Trying to access array offset on value of type null in /var/www/html/plugins/themes/default/DefaultThemePlugin.inc.php on line 163, referer: الدخول | مجلة جامعة المنارة

Noting that the version of OJS is : 3.3.0.4

Please Can you help with this problem?

Thank you.