Tiny fix : handles errors with creating new orders

[jordan-castelloe]

Description

This checks to see if users specify a payment_option_id when they create a new order. If they don't, it creates a payment_option_id with a value of null.

Number of Fixes

Fixes #115

Testing

1. Start your server.
2. POST the following JSON to localhost:8080/api/v1/orders: {"customer_id":1}
3. Check what id that returns and go GET the order with that id (localhost:8080/api/v1/orders/id)
4. The order should have a payment_option_id and the value should be null.

[kenziebottoms]

testing