Add validation and exception for weight to CartItem Constructor

src/CartItem.php

@@ -97,6 +97,9 @@ class CartItem implements Arrayable, Jsonable
         if (strlen($price) < 0 || !is_numeric($price)) {
             throw new \InvalidArgumentException('Please supply a valid price.');
         }
+        if (strlen($weight) < 0 || !is_numeric($weight)) {
+            throw new \InvalidArgumentException('Please supply a valid weight.');
+        }
 
         $this->id = $id;
         $this->name = $name;