Undefined variable: common_li_classes_flat

When I reduce my page down to mobile size I get an error printing on screen which says:

Notice: Undefined variable: common_li_classes_flat in /Users/michaelalockett/Documents/test sites/wp-content/plugins/woocommerce-menu-bar-cart/wp-menu-cart.php on line 382

Do you know what is causing this or how to get rid of the text?

https://wordpress.org/plugins/woocommerce-menu-bar-cart/