Spree: Skipping delivery step, but adding back default shipping method and tax calculation

README.md

Objective: Skip the delivery step in the Checkout state machine and bring back the ability to add a default shipping method and tax calculation

Approach: Add decorators to the Checkout controller and the Order model (see attached files)

Note: This approach might be better managed by overriding the self.define_state_machine! method of the Checkout model located at app/models/spree/order/checkout.rb. However, this model is rather unstable in the Spree upgrade path and overriding the above classes seems to be simpler to adjust.

checkout_controller_decorator.rb

# app/models/spree/checkout_controller_decorator.rb

Spree::CheckoutController.class_eval do

  def before_payment
    current_order.payments.destroy_all if request.put?
    @order.create_tax_charge!
    @order.shipping_method ||= (@order.rate_hash.first && @order.rate_hash.first[:shipping_method])
    @order.create_shipment!
    @order.update!
  end
  
end

order_decorator.rb

# app/models/spree/order_decorator.rb

Spree::Order.class_eval do
  
  ...
  
  checkout_flow do
    go_to_state :address
    # go_to_state :delivery <== remove this line
    go_to_state :payment, :if => lambda { |order| order.payment_required? }
    go_to_state :confirm, :if => lambda { |order| order.confirmation_required? }
    go_to_state :complete
    remove_transition :from => :delivery, :to => :confirm
  end

end

This is not working.

Error shows undefined method rate_hash and first for nil:nil_class.
Will you please a full model and controller code to skip delivery step but adding default shipping.