Error: Call to a member function getEntityTypeId()

Ran into another error if the $arg variable turns out to be a proper EntityInterface object. I put in another check to see if it's a proper entity, just add it to the array, but, also check if it's an int/str to make sure it's safe to pass to entity load.

Still not sure about this solution as a whole, but, it's fixing errors for us at the moment.

I found this issue when installing Notification message to our side crashed a view with contextual filters in the URL.

The error in our case was this

The website encountered an unexpected error. Try again later.

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "arg_0" entity type does not exist. in Drupal\Core\Entity\EntityTypeManager->getDefinition() (line 139 of core/lib/Drupal/Core/Entity/EntityTypeManager.php).

Drupal\Core\Entity\EntityTypeManager->getHandler() (Line: 192)
Drupal\Core\Entity\EntityTypeManager->getStorage() (Line: 129)
Drupal\notification_message\Cache\Context\RouteEntityUuidCacheContext->attachViewRouteEntities() (Line: 86)
Drupal\notification_message\Cache\Context\RouteEntityUuidCacheContext->entityCacheTagsFromRoute() (Line: 60)
Drupal\notification_message\Cache\Context\RouteEntityUuidCacheContext->getContext() (Line: 123)
Drupal\Core\Cache\Context\CacheContextsManager->convertTokensToKeys() (Line: 244)
Drupal\Core\Cache\VariationCache->createCacheIdFast() (Line: 175)
Drupal\Core\Cache\VariationCache->getRedirectChain() (Line: 35)
Drupal\Core\Cache\VariationCache->get() (Line: 71)
Drupal\Core\Render\RenderCache->get() (Line: 113)
Drupal\Core\Render\PlaceholderingRenderCache->get() (Line: 317)
Drupal\Core\Render\Renderer->doRender() (Line: 493)
Drupal\Core\Render\Renderer->doRender() (Line: 240)
Drupal\Core\Render\Renderer->render() (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 122)
__TwigTemplate_a80a95a6a8c5a3904dde60ae71cea77e->block_page_pre_content() (Line: 171)
Twig\Template->displayBlock() (Line: 130)
__TwigTemplate_f0b5e2f7c622ad70fb53191694409337->doDisplay() (Line: 394)
Twig\Template->displayWithErrorHandling() (Line: 367)
Twig\Template->display() (Line: 61)
__TwigTemplate_a80a95a6a8c5a3904dde60ae71cea77e->doDisplay() (Line: 394)
Twig\Template->displayWithErrorHandling() (Line: 367)
Twig\Template->display() (Line: 39)
__TwigTemplate_9e59da2f5f2329765a9dfd034cd52843->doDisplay() (Line: 394)
Twig\Template->displayWithErrorHandling() (Line: 367)
Twig\Template->display() (Line: 379)
Twig\Template->render() (Line: 38)
Twig\TemplateWrapper->render() (Line: 39)
twig_render_template() (Line: 348)
Drupal\Core\Theme\ThemeManager->render() (Line: 480)
Drupal\Core\Render\Renderer->doRender() (Line: 240)
Drupal\Core\Render\Renderer->render() (Line: 475)
Drupal\Core\Template\TwigExtension->escapeFilter() (Line: 81)
__TwigTemplate_cba7f8237d6b6745d5fea617efe7d916->doDisplay() (Line: 394)
Twig\Template->displayWithErrorHandling() (Line: 367)
Twig\Template->display() (Line: 39)
__TwigTemplate_f020d8f0b6dad9d1f81515d1f59f880c->doDisplay() (Line: 394)
Twig\Template->displayWithErrorHandling() (Line: 367)
Twig\Template->display() (Line: 379)
Twig\Template->render() (Line: 38)
Twig\TemplateWrapper->render() (Line: 39)
twig_render_template() (Line: 348)
Drupal\Core\Theme\ThemeManager->render() (Line: 480)
Drupal\Core\Render\Renderer->doRender() (Line: 240)
Drupal\Core\Render\Renderer->render() (Line: 158)
Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() (Line: 627)
Drupal\Core\Render\Renderer->executeInRenderContext() (Line: 153)
Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse() (Line: 90)
Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray()
call_user_func() (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch() (Line: 186)
Symfony\Component\HttpKernel\HttpKernel->handleRaw() (Line: 76)
Symfony\Component\HttpKernel\HttpKernel->handle() (Line: 58)
Drupal\Core\StackMiddleware\Session->handle() (Line: 48)
Drupal\Core\StackMiddleware\KernelPreHandle->handle() (Line: 28)
Drupal\Core\StackMiddleware\ContentLength->handle() (Line: 106)
Drupal\page_cache\StackMiddleware\PageCache->pass() (Line: 85)
Drupal\page_cache\StackMiddleware\PageCache->handle() (Line: 48)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle() (Line: 51)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle() (Line: 36)
Drupal\Core\StackMiddleware\AjaxPageState->handle() (Line: 51)
Drupal\Core\StackMiddleware\StackedHttpKernel->handle() (Line: 704)
Drupal\Core\DrupalKernel->handle() (Line: 19)

The patch in this issue fixed the problem. I would be willing to mark this RTBC and mark it Major or even Critical because it causes a crash. I will see if I can come up with another suggestion how to fix this.

I tried to improve the code a bit and made some small improvements. Here is an attached patch with following changes.

1. Added a check for $route_object being null to avoid potential errors.
2. Used instanceof instead of is_a for checking if $arg is an instance of EntityInterface.
3. Some small style changes.

Tested that the issue is still resolved.

I opened a MR for this for easier review and commenting.