Undefined index: HTTP_REFERER

I get the following notice in my debug log whenever I visit a page.
I use a plugin called “Make Paths Relative” to use relative paths throughout my site. Not sure if that has anything to do with it, but it would be great if you could provide a fix for that.

[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559
[31-Mar-2021 08:28:02 UTC] PHP Notice:  Undefined index: HTTP_REFERER in /home/www/testenv2/wp-content/plugins/user-access-manager/src/Wrapper/Wordpress.php on line 559