Merge pull request #5335 from solidusio/backport/v4.0/pr-5330

[v4.0] Fix error added when resetting order flow on an empty order

core/app/models/spree/order.rb

@@ -522,7 +522,7 @@ def restart_checkout_flow
         state: 'cart',
         updated_at: Time.current
       )
-      self.next
+      self.next if line_items.any?
     end
 
     def refresh_shipment_rates

core/spec/models/spree/order_spec.rb

@@ -579,10 +579,17 @@ def merge!(other_order, user = nil)
     end
 
     context "without line items" do
+      let(:order) { create(:order, state: "delivery", line_items: []) }
+
       it "updates the state column to cart" do
-        order = create(:order, state: "delivery")
         expect{ order.restart_checkout_flow }.to change{ order.state }.from("delivery").to("cart")
       end
+
+      it "doesn't add errors to the order" do
+        order.restart_checkout_flow
+
+        expect(order.errors).to be_empty
+      end
     end
   end