File records, files themselves lost in translation

I'm working on a project that someone else did，An error was encountered on commerce checkout completion, what I did is just add an file field(multi value) to order type.

Error mesaage:

The website encountered an unexpected error. Please try again later.
Error: Call to a member function hasTranslation() on null in Drupal\file\Plugin\Field\FieldType\FileFieldItemList->postSave() (line 54 of core/modules/file/src/Plugin/Field/FieldType/FileFieldItemList.php).
Drupal\file\Plugin\Field\FieldType\FileFieldItemList->postSave(1)
call_user_func_array(Array, Array) (Line: 938)
Drupal\Core\Entity\ContentEntityStorageBase->invokeFieldMethod('postSave', Object, 1) (Line: 970)
Drupal\Core\Entity\ContentEntityStorageBase->invokeFieldPostSave(Object, 1) (Line: 896)
Drupal\Core\Entity\ContentEntityStorageBase->invokeHook('update', Object) (Line: 56)
Drupal\commerce\CommerceContentEntityStorage->invokeHook('update', Object) (Line: 64)
Drupal\commerce_order\OrderStorage->invokeHook('update', Object) (Line: 598)
Drupal\Core\Entity\EntityStorageBase->doPostSave(Object, 1) (Line: 781)
Drupal\Core\Entity\ContentEntityStorageBase->doPostSave(Object, 1) (Line: 523)
Drupal\Core\Entity\EntityStorageBase->save(Object) (Line: 804)
Drupal\Core\Entity\Sql\SqlContentEntityStorage->save(Object) (Line: 339)
Drupal\Core\Entity\EntityBase->save() (Line: 429)
Drupal\commerce_checkout\Plugin\Commerce\CheckoutFlow\CheckoutFlowBase->submitForm(Array, Object) (Line: 614)
Drupal\commerce_checkout\Plugin\Commerce\CheckoutFlow\CheckoutFlowWithPanesBase->submitForm(Array, Object)
call_user_func_array(Array, Array) (Line: 114)
Drupal\Core\Form\FormSubmitter->executeSubmitHandlers(Array, Object) (Line: 52)
Drupal\Core\Form\FormSubmitter->doSubmitForm(Array, Object) (Line: 597)
Drupal\Core\Form\FormBuilder->processForm('commerce_checkout_flow_multistep_default', Array, Object) (Line: 325)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 224)
Drupal\Core\Form\FormBuilder->getForm(Object, 'review') (Line: 143)
Drupal\commerce_checkout\Controller\CheckoutController->formPage(Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 580)
Drupal\Core\Render\Renderer->executeInRenderContext(Object, Object) (Line: 124)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->wrapControllerExecutionInRenderContext(Array, Array) (Line: 97)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 169)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 38)
Drupal\webprofiler\StackMiddleware\WebprofilerMiddleware->handle(Object, 1, 1) (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 718)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

I haven't got which cause this problem, but the code change of this issue's commit has some flaw here:
if ($original->hasTranslation($langcode))
It didn't check whether the $original is null.

I have create a new issue for it