/*
Submit a free cart transaction

This an helper method to be used for when we want to make a
quick (free) transaction without a valid payment method.
The default payment method for free carts is used here.

{cart} [partialCart] - A cart-like object. We just need a valid `product_slug` property for cart items
{function} [onComplete] Callback function called on completion
function submitFreeTransaction( partialCart, onComplete ) {
	const cart = fillInAllCartItemAttributes( partialCart, productsList.get() ),
		transaction = {
			payment: fullCreditsPayment,
		};

	submitTransaction( { cart, transaction }, onComplete );
}