Checked if the entity has id

Closes #3462086

hreflang.module

@@ -26,17 +26,19 @@ function hreflang_page_attachments(array &$page): void {
   $is_front_page = \Drupal::service('path.matcher')->isFrontPage();
   if ($config->get('defer_to_content_translation') && $entity = hreflang_content_translation_get_entity()) {
     if ($addXDefault) {
-      $url = $is_front_page ? Url::fromRoute('<front>') : $entity->toUrl();
-      $page['#attached']['html_head_link'][] = [
-        [
-          'rel' => 'alternate',
-          'hreflang' => 'x-default',
-          'href' => $url
-            ->setOption('language', $entity->getUntranslated()->language())
-            ->setAbsolute()
-            ->toString(),
-        ],
-      ];
+      if($entity->id()) {
+        $url = $is_front_page ? Url::fromRoute('<front>') : $entity->toUrl();
+        $page['#attached']['html_head_link'][] = [
+          [
+            'rel' => 'alternate',
+            'hreflang' => 'x-default',
+            'href' => $url
+              ->setOption('language', $entity->getUntranslated()->language())
+              ->setAbsolute()
+              ->toString(),
+          ],
+        ];
+      }
     }
     return;
   }