jQuery Error

On the website console there is js error.
See this screenshot: https://paste.pics/ac76eae5ca6c886e98ab6f4f3299881b

I would request you to please fix this asap.

I have fixed this by editing the plugin’s file as temporary fix for my site.
I have added this code:

if (wcj_checkout_core_field.class == null){}else{
  jQuery(this).addClass(wcj_checkout_core_field.class[0]);
}

Added the above condition for check if variable is null or not.

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