diff -u b/core/lib/Drupal/Core/Config/ConfigManager.php b/core/lib/Drupal/Core/Config/ConfigManager.php
--- b/core/lib/Drupal/Core/Config/ConfigManager.php
+++ b/core/lib/Drupal/Core/Config/ConfigManager.php
@@ -17,7 +17,6 @@
 use Drupal\Core\StringTranslation\TranslationManager;
 use Symfony\Component\EventDispatcher\EventDispatcherInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
-use Drupal\Core\Extension\ThemeHandlerInterface;
 
 /**
  * The ConfigManager provides helper functions for the configuration system.
@@ -348,13 +347,7 @@
     // @todo ThemeHandler cannot be injected into ConfigManager, since that
     // causes a circular service dependency.
     $themes = \Drupal::service('theme_handler')->listInfo();
-    foreach ($names as $theme_name) {
-      if (!isset($themes[$theme_name])) {
-        return FALSE;
-      }
-    }
-
-    return TRUE;
+    return !((bool) array_diff($names, array_keys($themes)));
   }
 
   /**
@@ -368,8 +361,7 @@
   protected function validateConfigEntityDependentEntitiesExistence(array $names) {
     foreach ($names as $config_name) {
       // Run over all entity type dependencies and fail as soon as possible.
-      $entity = $this->getEntityByConfigName($config_name);
-      if (empty($entity)) {
+      if (!$this->getEntityByConfigName($config_name)) {
         return FALSE;
       }
     }