Warning: array_key_exists() expects parameter 2 to be array…

Everyone can see this error message on top of the Forum page, but no other page. Therefore, I think it is related to the foro plugin:

Warning: array_key_exists() expects parameter 2 to be array, boolean given in /home/univer73/public_html/universalsolder/wp-content/plugins/wordpress-seo-premium/frontend/class-json-ld.php on line 117

How to fix this?

Thanks

The page I need help with: [log in to see the link]