Errors in PHP log

Hi.

I am seeing the following errors in my PHP error log, and they seem to be originating from your plugin:

WordPress database error You have an error in your SQL syntax; check the manual that corresponds to your MariaDB server version for the right syntax to use near '' at line 1 for query SELECT referral_parent FROM wp_referal_users WHERE user_id= made by wp_delete_user, do_action('delete_user'), WP_Hook->do_action, WP_Hook->apply_filters, Referal_Users->delete_user_callback, Referal_Users->fnUpdateFollowersCount

Should I be concerned, and what can be done to resolve the errors?

Thanks.