I get the following error when visiting a clients WPForms panel in admin:

Fatal error: Uncaught Error: Call to a member function get() on null in
/var/www/example.com/public_html/wp-includes/query.php:28 Stack trace: #0
/var/www/example.com/public_html/wp-content/plugins/piklist/includes/class-piklist-wordpress.php(610): get_query_var('taxonomy_relati...') #1 
/var/www/example.com/public_html/wp-includes/class-wp-hook.php(305): 
Piklist_WordPress::relation_taxonomy(' AND wp_p...') #2 
/var/www/example.com/public_html/wp-includes/plugin.php(233): WP_Hook->apply_filters(' AND
 wp_p...', Array) #3 /var/www/example.com/public_html/wp-includes/class-wp-
query.php(2568): apply_filters_ref_array('posts_where', Array) #4 
/var/www/example.com/public_html/wp-includes/class-wp-query.php(3465): WP_Query-
>get_posts() #5 /var/www/example.com/public_html/wp-includes/post.php(2228): WP_Query-
>query(Array) #6 /var/www/example.com/public_html/wp-
content/plugins/wpforms/includes/class-form.php(225): get_posts(Array) #7 
/var/www/example.com/public_html/wp-content/plugins/wpforms/i in 
/var/www/example.com/public_html/wp-includes/query.php on line 28

How can I quikly fix it?