This is the error message

Deprecated functionality: preg_replace(): Passing null to parameter #3 ($subject) of type array|string is deprecated in /var/www/html/app/code/core/Mage/Adminhtml/Block/System/Config/Form/Field.php on line 45

// replace [value] with [inherit]
        $namePrefix = preg_replace('#\[value\](\[\])?$#', '', $element->getName());

I am getting this error when running extension MageWorx SEO Suite Ultimate. Just accesss Backend > System > Config > MageWorx Extensions & Support to get it. Maybe other extensions could produce the same issue.

It must be

// replace [value] with [inherit]
        $namePrefix = preg_replace('#\[value\](\[\])?$#', '', (string) $element->getName()'');