Fix fatal errors

Here is a first patch. I got stuck on this error:

Drupal\Component\Plugin\Exception\PluginNotFoundException: The "nothing" plugin does not exist. in Drupal\Core\Plugin\DefaultPluginManager->doGetDefinition() (line 52 of core/lib/Drupal/Component/Plugin/Discovery/DiscoveryTrait.php).

Drupal\Core\Plugin\DefaultPluginManager->getDefinition('Nothing') (Line: 16)
Drupal\Core\Plugin\Factory\ContainerFactory->createInstance('Nothing', Array) (Line: 84)
Drupal\Component\Plugin\PluginManagerBase->createInstance('Nothing', Array) (Line: 120)
Drupal\entity_labels\AutomaticValueManager->getInstance(Array) (Line: 231)
Drupal\entity_labels\AutomaticValueManager->load('block_content') (Line: 233)
Drupal\entity_labels\EntityLabelsManager->buildEntityTypeInfo(Object) (Line: 215)
Drupal\entity_labels\EntityLabelsManager->buildInfo() (Line: 183)
Drupal\entity_labels\EntityLabelsManager->getInfo() (Line: 74)
Drupal\entity_labels\Controller\EntityLabelsController->adminOverview()
call_user_func_array(Array, Array) (Line: 123)
Drupal\Core\EventSubscriber\EarlyRenderingControllerWrapperSubscriber->Drupal\Core\EventSubscriber\{closure}() (Line: 574)
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}()
call_user_func_array(Object, Array) (Line: 144)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 64)
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: 99)
Drupal\page_cache\StackMiddleware\PageCache->pass(Object, 1, 1) (Line: 78)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 47)
Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 50)
Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23)
Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 649)
Drupal\Core\DrupalKernel->handle(Object) (Line: 19)

I guess the plugin stystem changed somehow. I am not too familiar with it. Could someone step in?