diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
index b2d6625..a088a8b 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscoveryParser.php
@@ -97,15 +97,9 @@ public function buildByExtension($extension) {
       }
       else {
         $message = sprintf('The extension "%s" is not available.', $extension);
-
-        \Drupal\Component\Assertion\Handle::register();
         assert(false, $message);
-
         trigger_error($message, E_USER_WARNING);
-        if(function_exists('drupal_set_message')) {
-          drupal_set_message($message, 'error');
-        }
-        return NULL;
+        return;
       }
       $path = $this->drupalGetPath($extension_type, $extension);
     }