Fix issue: Error: Call to a member function hasItem() on null in Drupal\commerce_simple_stock\EventSubscriber\OrderEventSubscriber->onOrderUpdate()

Patch #2 fixes the issue for me. Thanks.

This part is wrong.

-
+    if ($item->getOriginal == NULL || $item == NULL) {
+      return;
+    }
     if ($order && !in_array($order->getState()->value, ['draft', 'canceled'])) {

$item->getOriginal is always going to return null. Im not sure what its trying to accomplish here.

@loze is right, that snippet always will be true, and the return will be executed.

$item cannot be null (since it triggers the event), so the check just can be:

    if ($item->original) {
      return;
    }
    if ($order && !in_array($order->getState()->value, ['draft', 'canceled'])) {

      $diff = $item->original->getQuantity() - $item->getQuantity();

for avoiding the warning if $item->Original is NULL.

The code that truly fixes the issue error is the other snippet contained in the patch:

@@ -158,7 +160,7 @@ class OrderEventSubscriber implements EventSubscriberInterface {
    */
   public function onOrderUpdate(OrderEvent $event) {
     $order = $event->getOrder();
-    $original_order = $order->original;
+    $original_order = empty($order->original) ? $order : $order->original;
     $allow_negative = \Drupal::config('commerce_simple_stock.settings')->get('allow_backorder');
 
     if ($original_order) {

I have implemented the modifications as per issue #6. please review the patch.