Add Product to Cart - AJAX Error

[smileservices]

1. Install GoCart3
2. Set up new category
3. Add Product
4. Go to frontend
5. Select category > product
6. Click "Add To Cart"
7. AJAX Error : jquery.js: 6 POST http://gocart3/cart/add-to-cart 500 (Internal Server Error)

Error Number: 1366

Incorrect decimal value: '' for column 'total_weight' at row 1

INSERT INTO order_items (sku, name, slug, description, excerpt, free_shipping, shippable, taxable, fixed_quantity, weight, track_stock, images, is_giftcard, enabled_1, price_1, saleprice_1, saleprice, price, product_id, type, hash, coupon_discount, coupon_discount_quantity, coupon_code, order_id, quantity, total_price, total_weight) VALUES ('', 'BBC News', 'bbc-news', '', '', '0', '1', '1', '1', '', '1', '[]', '0', '1', '100.00', '90.00', '90.00', '100.00', '1', 'product', '8018f419dce7901430c84dee46169bc5', 0, 0, '', '1', 1, '90.00', '')
Filename: ...gocart3/application/modules/orders/models/Orders.php
Line Number: 341