checkout.session.completed If payment_status is no_payment_required , then don't attempt currency (or other) invalid property accesses

[chrisjsimpson]

Is your feature request related to a problem? Please describe.

Stripe event checkout.session.completed may not always have a currency, for example when payment_status is no_payment_required.

no_payment_required Docs:

The payment is delayed to a future date, or the Checkout Session is in setup mode and doesn’t require a payment at this time.

subscribie/blueprints/checkout/__init__.py", line 857, in stripe_webhook                                                
    currency = session["currency"].upper()                                                                                                                                                    
               ^^^^^^^^^^^^^^^^^^^^^^^^^                                                                                                                                                      
AttributeError: 'NoneType' object has no attribute 'upper'  

Describe the solution you'd like

If payment_status is no_payment_required , then don't attempt currency (or other) invalid property accesses.

Describe alternatives you've considered

Additional context

subscribie/subscribie/blueprints/checkout/__init__.py

Line 857 in 29fa7c5

currency = session["currency"].upper()