Issue #3270979: Wrong usage of null coealescing operator in DropdownLanguage.php

src/Plugin/Block/DropdownLanguage.php

@@ -144,7 +144,8 @@ class DropdownLanguage extends BlockBase implements ContainerFactoryPluginInterf
       $derivative_id = $this->getDerivativeId();
       $route = $this->pathMatcher->isFrontPage() ? '<front>' : '<current>';
       $current_language = $this->languageManager->getCurrentLanguage($derivative_id)->getId();
-      $links = $this->languageManager->getLanguageSwitchLinks($derivative_id, Url::fromRoute($route))->links;
+      $languageSwitchLinksObject = $this->languageManager->getLanguageSwitchLinks($derivative_id, Url::fromRoute($route));
+      $links = ($languageSwitchLinksObject !== NULL) ? $languageSwitchLinksObject->links : [];
 
       // Place active language ontop of list.
       if (isset($links[$current_language])) {