qty required on notional orders

**Describe the bug**
It appears that despite the docs [stating](https://github.com/alpacahq/user-docs/blob/c14e3a349cbfbcefb5a87d9078f1cf704c74a825/data/webapi/entities/order-v2.yaml#L41) that setting `notional` on a new order implicitly sets `qty` to `null`, that is not actually what happens:
```yaml
- name: notional
type: string
desc: Ordered notional amount. If entered, `qty` will be null. Can take up to 9 decimal points.
```

What we see:
```sh
curl -X POST -H "APCA-API-KEY-ID: $APCA_API_KEY_ID" -H "APCA-API-SECRET-KEY: $APCA_API_SECRET_KEY" -H "Content-Type: application/json" https://paper-api.alpaca.markets/v2/orders --data '{"symbol":"SPY","notional":"3333333.33333333","side":"buy","order_class":"simple","type":"market","time_in_force":"day","limit_price":null,"stop_price":null,"trail_price":null,"trail_percent":null,"take_profit":null,"stop_loss":null,"extended_hours":false,"client_order_id":null}'
{"code":40010001,"message":"qty is required"}
```
Interestingly, I couldn't even get it working with `qty` being `null`. Has anybody actually tested the `notional` stuff?

**To Reproduce**
Steps to reproduce the behavior:
```sh
curl -X POST -H "APCA-API-KEY-ID: $APCA_API_KEY_ID" -H "APCA-API-SECRET-KEY: $APCA_API_SECRET_KEY" -H "Content-Type: application/json" https://paper-api.alpaca.markets/v2/orders --data '{"symbol":"SPY","notional":"3333333.33333333","side":"buy","order_class":"simple","type":"market","time_in_force":"day","limit_price":null,"stop_price":null,"trail_price":null,"trail_percent":null,"take_profit":null,"stop_loss":null,"extended_hours":false,"client_order_id":null}'
```

**Expected behavior**
The order should go through.