Notice: Undefined index:

I get these errors when I just installed the latest version on my localhost, not sure how to solve them. I found that one solution would be the use of “isset” but I got these in the plugin, I didnt even add my own code yet..?

Notice: Undefined index: addcart in /Users/bara/Sites/wordpress/wp-content/plugins/wp-ultra-simple-paypal-shopping-cart/wp_ultra_simple_shopping_cart.php on line 87

Notice: Undefined index: quantity in /Users/bara/Sites/wordpress/wp-content/plugins/wp-ultra-simple-paypal-shopping-cart/wp_ultra_simple_shopping_cart.php on line 134

Notice: Undefined index: delcart in /Users/bara/Sites/wordpress/wp-content/plugins/wp-ultra-simple-paypal-shopping-cart/wp_ultra_simple_shopping_cart.php on line 147

https://www.ads-software.com/extend/plugins/wp-ultra-simple-paypal-shopping-cart/