log error

Hi,
you made one of my favourite plugin ever.
I’m using Contextual related post on all my web sites.
Recently i notice this message in my apache log file.

[Sat Jul 21 10:53:32.509116 2018] [:error] [pid 14540] [client xxx.xxx.79.2:61693] PHP Warning: explode() expects parameter 2 to be string, object given in /var/www/html/wp-content/plugins/contextual-related-posts/includes/main-query.php on line 420

Where line 420 in my installation is like this:

$exclude_post_ids = explode( ‘,’, $args[‘exclude_post_ids’] );

I’m running WP on Ubuntu 16.04, PHP 7.0
Any idea on how to fix this?

Thank you