Fix calculate_price when order_item without product is provided

app/models/order.rb

@@ -36,7 +36,7 @@ class Order < ActiveRecord::Base
   private
 
     def calculate_price
-      self.price_cents = self.order_items.map{ |oi| oi.count * oi.product.price_cents }.sum
+      self.price_cents = self.order_items.map{ |oi| oi.count * (oi.product.try(:price_cents) || 0) }.sum
     end
 
     def create_api_job

spec/models/order_spec.rb

@@ -48,7 +48,7 @@ describe Order do
 
     describe 'order_items' do
       it 'should be validated' do
-        @order.order_items << OrderItem.new(count: -5)
+        @order.order_items.build(count: -5)
         expect(@order).to_not be_valid
       end
     end