Error message

Notice: Undefined index: US in Drupal\certina_redirect\Plugin\LanguageNegotiation\CertinaNegotiationLanguageNegotiation->_getMatchCountryToLanguage() (line 170 of modules/custom/certina_redirect/src/Plugin/LanguageNegotiation/CertinaNegotiationLanguageNegotiation.php).
Drupal\certina_redirect\Plugin\LanguageNegotiation\CertinaNegotiationLanguageNegotiation->_getMatchCountryToLanguage('US') (Line: 106)
Drupal\certina_redirect\Plugin\LanguageNegotiation\CertinaNegotiationLanguageNegotiation->_getLanguageByCountryCode() (Line: 50)
Drupal\certina_redirect\Plugin\LanguageNegotiation\CertinaNegotiationLanguageNegotiation->getLangcode(Object) (Line: 186)
Drupal\language\LanguageNegotiator->negotiateLanguage('language_interface', 'certina-language-negotiation') (Line: 131)
Drupal\language\LanguageNegotiator->initializeType('language_interface') (Line: 218)
Drupal\language\ConfigurableLanguageManager->getCurrentLanguage() (Line: 77)
Drupal\language\EventSubscriber\LanguageRequestSubscriber->onKernelRequestLanguage(Object, 'kernel.request', Object) (Line: 111)
Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch('kernel.request', Object) (Line: 116)
Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 57)
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: 207)
Drupal\page_cache\StackMiddleware\PageCache->fetch(Object, 1, 1) (Line: 121)
Drupal\page_cache\StackMiddleware\PageCache->lookup(Object, 1, 1) (Line: 75)
Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 79)
Drupal\certina_prerender\PrerenderMiddleware->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: 663)
Drupal\Core\DrupalKernel->handle(Object) (Line: 20)

Glückwunsch, Ole Einar Bjørndalen!