Notice: Undefined variable: source_langcode in Drupal\content_translation\ContentTranslationHandler->entityFormAlter()

When I enable translation for a content type. And then create a node of that type and then when I edit that node, I see the following notice on my site.

Notice: Undefined variable: source_langcode in Drupal\content_translation\ContentTranslationHandler->entityFormAlter() (line 415 of core/modules/content_translation/src/ContentTranslationHandler.php).

Drupal\content_translation\ContentTranslationHandler->entityFormAlter(Array, Object, Object) (Line: 18)
Drupal\node\NodeTranslationHandler->entityFormAlter(Array, Object, Object) (Line: 400)
content_translation_form_alter(Array, Object, 'node_living_unit_edit_form') (Line: 539)
Drupal\Core\Extension\ModuleHandler->alter('form', Array, Object, 'node_living_unit_edit_form') (Line: 836)
Drupal\Core\Form\FormBuilder->prepareForm('node_living_unit_edit_form', Array, Object) (Line: 418)
Drupal\Core\Form\FormBuilder->rebuildForm('node_living_unit_edit_form', Object, Array) (Line: 627)
Drupal\Core\Form\FormBuilder->processForm('node_living_unit_edit_form', Array, Object) (Line: 320)
Drupal\Core\Form\FormBuilder->buildForm(Object, Object) (Line: 91)
Drupal\Core\Controller\FormController->getContentResult(Object, Object)
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 573)
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: 151)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 68)
Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 57)
Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 52)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 694)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

I updated the Drupal core using composer from 8.8.0 with the following steps

composer update drupal/core:^8.8.1 --with-dependencies