Shipment tax adjustments not created when using Paypal Express

[mdavo6]

When using Paypal Express our checkout flow skips the payment step. For example our checkout flow is:

1. Address
2. Delivery
3. Confirm
4. Complete

In Spree's checkout.rb model, "create_tax_charge!" is called when an order progresses through the payment step, however in our case (and I assume most use cases for Paypal Express) this is never called due to the lack of a payment step. This leads to tax adjustments on shipping not being calculated.

To resolve I have added the following line to an order_decorator to ensure create_tax_charge! is called:
state_machine.before_transition to: :confirm, from: :delivery, do: :create_tax_charge!
I have added the call between the delivery and before the confirm to ensure it is only called when a checkout skips the payment step, however perhaps there may be another better time to call it?