In the WPC Smart Attribute Groups plugin, version 1.0.2:

The function parse_term_query in the class-backend.php does not check if the value is NULL before trying to access the array in line 234:

        $taxonomy = $query->query_vars['taxonomy'][0];

This results in a PHP error being written on our site, along the lines of:
"Trying to access array offset on value of type null".

I solved the issue locally for now by adding the following check before and returning from the function early, if the query is NULL, like so:

        if (!isset($query->query_vars['taxonomy'])) {
            return;
        }
            
        $taxonomy = $query->query_vars['taxonomy'][0];

Would be of course better, if you could fix this in the plugin itself.

Thank you in advance!