Simplify by moving conditional to guard clause

app/controllers/api/v0/shipments_controller.rb

@@ -21,11 +21,9 @@ module Api
         @shipment.refresh_rates
         @shipment.save!
 
-        if @order.line_items.any? && @order.state.in?(["cart", "address", "delivery"])
-          OrderWorkflow.new(@order).advance_to_payment
-        end
+        OrderWorkflow.new(@order).advance_to_payment if @order.line_items.any?
 
-        render json: @shipment.reload, serializer: Api::ShipmentSerializer, status: :ok
+        render json: @shipment, serializer: Api::ShipmentSerializer, status: :ok
       end
 
       def update

app/controllers/spree/admin/orders/customer_details_controller.rb

@@ -25,7 +25,7 @@ module Spree
 
             refresh_shipment_rates
             recalculate_taxes
-            OrderWorkflow.new(@order).advance_to_payment if @order.state.in? ["cart", "address", "delivery"]
+            OrderWorkflow.new(@order).advance_to_payment
 
             flash[:success] = Spree.t('customer_details_updated')
             redirect_to spree.admin_order_customer_path(@order)

app/controllers/spree/admin/orders_controller.rb

@@ -51,7 +51,8 @@ module Spree
           return redirect_to spree.edit_admin_order_path(@order)
         end
 
-        OrderWorkflow.new(@order).advance_to_payment if @order.state.in? ["cart", "address", "delivery"]
+        OrderWorkflow.new(@order).advance_to_payment
+
         if @order.complete?
           redirect_to spree.edit_admin_order_path(@order)
         else

app/services/order_workflow.rb

@@ -24,6 +24,8 @@ class OrderWorkflow
   end
 
   def advance_to_payment
+    return unless order.state.in? ["cart", "address", "delivery"]
+
     advance_to_state("payment", advance_order_options)
   end