diff --git a/core/includes/theme.inc b/core/includes/theme.inc
index 13a5154..37a7bb5 100644
--- a/core/includes/theme.inc
+++ b/core/includes/theme.inc
@@ -1222,8 +1222,6 @@ function _template_preprocess_default_variables() {
   // Variables that don't depend on a database connection.
   $variables = array(
     'attributes' => array(),
-    'title_attributes' => array(),
-    'content_attributes' => array(),
     'title_prefix' => array(),
     'title_suffix' => array(),
     'db_is_active' => !defined('MAINTENANCE_MODE'),
@@ -1584,6 +1582,9 @@ function template_preprocess_field(&$variables, $hook) {
     $variables['items'][$delta]['attributes'] = !empty($element['#items'][$delta]->_attributes) ? new Attribute($element['#items'][$delta]->_attributes) : clone($default_attributes);
     $delta++;
   }
+
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : clone $default_attributes;
+  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : clone $default_attributes;
 }
 
 /**
diff --git a/core/lib/Drupal/Core/Theme/ThemeManager.php b/core/lib/Drupal/Core/Theme/ThemeManager.php
index 6850fcb..aa8ed7c 100644
--- a/core/lib/Drupal/Core/Theme/ThemeManager.php
+++ b/core/lib/Drupal/Core/Theme/ThemeManager.php
@@ -355,15 +355,13 @@ protected function theme($hook, $variables = array()) {
       if (!isset($default_attributes)) {
         $default_attributes = new Attribute();
       }
-      foreach (array('attributes', 'title_attributes', 'content_attributes') as $key) {
-        if (isset($variables[$key]) && !($variables[$key] instanceof Attribute)) {
-          if ($variables[$key]) {
-            $variables[$key] = new Attribute($variables[$key]);
-          }
-          else {
-            // Create empty attributes.
-            $variables[$key] = clone $default_attributes;
-          }
+      if (isset($variables['attributes']) && !($variables['attributes'] instanceof Attribute)) {
+        if ($variables['attributes']) {
+          $variables['attributes'] = new Attribute($variables['attributes']);
+        }
+        else {
+          // Create empty attributes.
+          $variables['attributes'] = clone $default_attributes;
         }
       }
 
diff --git a/core/modules/block/block.module b/core/modules/block/block.module
index f9dd787..1205ce8 100644
--- a/core/modules/block/block.module
+++ b/core/modules/block/block.module
@@ -12,6 +12,7 @@
 use Drupal\language\ConfigurableLanguageInterface;
 use Drupal\system\Entity\Menu;
 use Drupal\block\Entity\Block;
+use Drupal\Core\Template\Attribute;
 
 /**
  * Implements hook_help().
@@ -257,6 +258,8 @@ function template_preprocess_block(&$variables) {
     $variables['attributes']['aria-describedby'] = $variables['title_attributes']['id'];
   }
 
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : new Attribute();
+  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : new Attribute();
 }
 
 /**
diff --git a/core/modules/comment/comment.module b/core/modules/comment/comment.module
index ea918bd..9f5ed06 100644
--- a/core/modules/comment/comment.module
+++ b/core/modules/comment/comment.module
@@ -24,6 +24,7 @@
 use Drupal\Core\Entity\Display\EntityViewDisplayInterface;
 use Drupal\Core\Field\FieldDefinitionInterface;
 use Drupal\Core\Render\Element;
+use Drupal\Core\Template\Attribute;
 use Drupal\Core\Url;
 use Drupal\field\Entity\FieldStorageConfig;
 use Drupal\field\FieldConfigInterface;
@@ -708,6 +709,8 @@ function template_preprocess_comment(&$variables) {
 
   // Add comment author user ID. Necessary for the comment-by-viewer library.
   $variables['attributes']['data-comment-user-id'] = $comment->getOwnerId();
+  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : new Attribute();
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : new Attribute();
 }
 
 /**
diff --git a/core/modules/search/search.pages.inc b/core/modules/search/search.pages.inc
index b50a6cd..dba393a 100644
--- a/core/modules/search/search.pages.inc
+++ b/core/modules/search/search.pages.inc
@@ -7,6 +7,7 @@
 
 use Drupal\Component\Utility\SafeMarkup;
 use Drupal\Core\Language\LanguageInterface;
+use Drupal\Core\Template\Attribute;
 
 /**
  * Implements hook_theme_suggestions_HOOK().
@@ -64,5 +65,7 @@ function template_preprocess_search_result(&$variables) {
     '#template' => '{{ info|safe_join(" - ") }}',
     '#context' => array('info' => $info),
   );
+  $variables['title_attributes'] = isset($variables['title_attributes']) ? new Attribute($variables['title_attributes']) : new Attribute();
+  $variables['content_attributes'] = isset($variables['content_attributes']) ? new Attribute($variables['content_attributes']) : new Attribute();
 }