Notice: Undefined offset:

I experienced the same issue on pages that have no node class.
There was simply a check missing if $classes is not empty.
Patch against the latest dev attached.

The patch is so simple one can easily apply it by hand by changing line 54 of node_class.module from

$variables['attributes']['class'][] = $classes['0']['value'];

to

if(!empty($classes)) {
      $variables['attributes']['class'][] = $classes['0']['value'];
    }

i proof: #2 works for me.
Thank valor & eigentor.

Patch was not committed, while code changed. Here is an update to date patch (826911-undefined-offset-2.patch), which works for me (just the line number changed). Please commit the patch, it's a very small and simple fix.

#4 works fine.
Thanks for the patch.
Marking as RTBC.

Thanks for the patch

Experienced this software problem with most Node Class 8.x-1.0-beta1 version:

Notice: Undefined offset: 0 in node_class_preprocess_node() (line 58 of /home/{site}/modules/node_class/node_class.module) #0 /home/{site}/core/includes/bootstrap.inc(566): _drupal_error_handler_real(8, 'Undefined offse...', '/home/uuuuviwu/...', 58, Array) #1 /home/{site}/modules/node_class/node_class.module(58): _drupal_error_handler(8, 'Undefined offse...', '/home/uuuuviwu/...', 58, Array) #2 /home/{site}/core/lib/Drupal/Core/Theme/ThemeManager.php(287): node_class_preprocess_node(Array, 'node', Array) #3 /home/{site}/core/lib/Drupal/Core/Render/Renderer.php(435): Drupal\Core\Theme\ThemeManager->render('node', Array) #4 /home/{site}/core/lib/Drupal/Core/Render/Renderer.php(195): Drupal\Core\Render\Renderer->doRender(Array, false) #5 /home/{site}/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(226): Drupal\Core\Render\Renderer->render(Array, false) #6 /home/{site}/core/lib/Drupal/Core/Render/Renderer.php(574): Drupal\Core\Render\MainContent\HtmlRenderer->Drupal\Core\Render\MainContent\{closure}() #7 /home/{site}/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(227): Drupal\Core\Render\Renderer->executeInRenderContext(Object(Drupal\Core\Render\RenderContext), Object(Closure)) #8 /home/{site}/core/lib/Drupal/Core/Render/MainContent/HtmlRenderer.php(117): Drupal\Core\Render\MainContent\HtmlRenderer->prepare(Array, Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\CurrentRouteMatch)) #9 /home/{site}/core/lib/Drupal/Core/EventSubscriber/MainContentViewSubscriber.php(90): Drupal\Core\Render\MainContent\HtmlRenderer->renderResponse(Array, Object(Symfony\Component\HttpFoundation\Request), Object(Drupal\Core\Routing\CurrentRouteMatch)) #10 /home/{site}/core/lib/Drupal/Component/EventDispatcher/ContainerAwareEventDispatcher.php(111): Drupal\Core\EventSubscriber\MainContentViewSubscriber->onViewRenderArray(Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent), 'kernel.view', Object(Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher)) #11 /home/{site}/vendor/symfony/http-kernel/HttpKernel.php(149): Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.view', Object(Symfony\Component\HttpKernel\Event\GetResponseForControllerResultEvent)) #12 /home/{site}/vendor/symfony/http-kernel/HttpKernel.php(64): Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object(Symfony\Component\HttpFoundation\Request), 1) #13 /home/{site}/core/lib/Drupal/Core/StackMiddleware/Session.php(57): Symfony\Component\HttpKernel\HttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #14 /home/{site}/core/lib/Drupal/Core/StackMiddleware/KernelPreHandle.php(47): Drupal\Core\StackMiddleware\Session->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #15 /home/{site}/core/modules/page_cache/src/StackMiddleware/PageCache.php(99): Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #16 /home/{site}/core/modules/page_cache/src/StackMiddleware/PageCache.php(78): Drupal\page_cache\StackMiddleware\PageCache->pass(Object(Symfony\Component\HttpFoundation\Request), 1, true) #17 /home/{site}/core/modules/ban/src/BanMiddleware.php(50): Drupal\page_cache\StackMiddleware\PageCache->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #18 /home/{site}/core/lib/Drupal/Core/StackMiddleware/ReverseProxyMiddleware.php(47): Drupal\ban\BanMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #19 /home/{site}/core/lib/Drupal/Core/StackMiddleware/NegotiationMiddleware.php(50): Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #20 /home/{site}/vendor/stack/builder/src/Stack/StackedHttpKernel.php(23): Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #21 /home/{site}/core/lib/Drupal/Core/DrupalKernel.php(656): Stack\StackedHttpKernel->handle(Object(Symfony\Component\HttpFoundation\Request), 1, true) #22 /home/{site}/index.php(19): Drupal\Core\DrupalKernel->handle(Object(Symfony\Component\HttpFoundation\Request)) #23 {main}.

Has the software problem above been fixed in the more recent dev branch release of this module?
When will a fix for this problem be available on the beta release branch of this module?