ENGCOM-6809: Update getCustomer method in order class #26423

 - Merge Pull Request #26423 from sertlab/magento2:FS/getcustomer-returns-null-25269
 - Merged commits:
   1. 92816ab
   2. 427a4ad
   3. f8bcd47
   4. 80c737a
   5. 5a1f48e
   6. 57e2532
   7. 3ca45d8

Author: magento-engcom-team

app/code/Magento/Sales/Model/Order.php

@@ -51,7 +51,7 @@
  * @method bool hasCustomerNoteNotify()
  * @method bool hasForcedCanCreditmemo()
  * @method bool getIsInProcess()
- * @method \Magento\Customer\Model\Customer getCustomer()
+ * @method \Magento\Customer\Model\Customer|null getCustomer()
  * @method \Magento\Sales\Model\Order setSendEmail(bool $value)
  * @SuppressWarnings(PHPMD.ExcessivePublicCount)
  * @SuppressWarnings(PHPMD.TooManyFields)
@@ -1326,7 +1326,7 @@ public function getTrackingNumbers()
      */
     public function getShippingMethod($asObject = false)
     {
-        $shippingMethod = parent::getShippingMethod();
+        $shippingMethod = $this->getData('shipping_method');
         if (!$asObject || !$shippingMethod) {
             return $shippingMethod;
         } else {