fix(medusa): keep country_code when partially updating cart addresses (#2683)

**What**
- Fixes a bug where `country_code` was dropped when partially updating a shipping or billing address on a cart.

packages/medusa/src/services/__tests__/cart.js

@@ -1,12 +1,12 @@
 import _ from "lodash"
 import { MedusaError } from "medusa-core-utils"
 import { IdMap, MockManager, MockRepository } from "medusa-test-utils"
+import { FlagRouter } from "../../utils/flag-router"
 import CartService from "../cart"
 import { InventoryServiceMock } from "../__mocks__/inventory"
 import { LineItemAdjustmentServiceMock } from "../__mocks__/line-item-adjustment"
-import { FlagRouter } from "../../utils/flag-router"
-import { taxProviderServiceMock } from "../__mocks__/tax-provider"
 import { newTotalsServiceMock } from "../__mocks__/new-totals"
+import { taxProviderServiceMock } from "../__mocks__/tax-provider"
 
 const eventBusService = {
   emit: jest.fn(),
@@ -1100,7 +1100,7 @@ describe("CartService", () => {
         last_name: "James",
         address_1: "24 Dunks Drive",
         city: "Los Angeles",
-        country_code: "US",
+        country_code: "us",
         province: "CA",
         postal_code: "93011",
         phone: "+1 (222) 333 4444",

packages/medusa/src/services/cart.ts

@@ -1238,8 +1238,6 @@ class CartService extends TransactionBaseService {
       address = addressOrId as Address
     }
 
-    address.country_code = address.country_code?.toLowerCase() ?? null
-
     if (address.id) {
       cart.billing_address = await addrRepo.save(address)
     } else {
@@ -1284,11 +1282,11 @@ class CartService extends TransactionBaseService {
       address = addressOrId as Address
     }
 
-    address.country_code = address.country_code?.toLowerCase() ?? null
-
     if (
       address.country_code &&
-      !cart.region.countries.find(({ iso_2 }) => address.country_code === iso_2)
+      !cart.region.countries.find(
+        ({ iso_2 }) => address.country_code?.toLowerCase() === iso_2
+      )
     ) {
       throw new MedusaError(
         MedusaError.Types.INVALID_DATA,