WP debug error “Trying to access array offset on value of type null”

Hi,
after creating the first batch of folders and subfolders, I get a lot of notices from WP Debug (one for each main folder). They are all the same:

Notice: Trying to access array offset on value of type null in /var/www/vhosts/domain.com/httpdocs/wp-content/plugins/memphis-documents-library/includes/mdocs-functions.php on line 755

I think this has to do with newer PHP versions not accepting this code anymore. Is this something that needs fixing/will be fixed in the next update?

Thanks!

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