Error: array_key_exists() expects parameter 2 to be array

Hi, I am getting this php error since I updated all plugins and WP core.

: array_key_exists() expects parameter 2 to be array,null given in /home/***/public_html/***/wp-content/plugins/wp-math-captcha/includes/class-core.php on line 644

Am I the only one finding this error?
Please advise as to what I should do.
Thank you in advance 🙂

p.s. great plugin!