diff --git a/core/lib/Drupal/Core/Asset/LibraryDiscovery.php b/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
index 6d9c5a6..8977200 100644
--- a/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
+++ b/core/lib/Drupal/Core/Asset/LibraryDiscovery.php
@@ -92,10 +92,9 @@ public function getLibrariesByExtension($extension) {
    */
   public function getLibraryByName($extension, $name) {
     $library_name = $extension . '/' . $name;
-    // @todo store that a library does not exist.
     $this->findDefinitions();
 
-    if (empty($this->libraryDefinitions[$library_name])) {
+    if (isset($this->libraryDefinitions[$library_name])) {
       $this->libraryDefinitions[$library_name] = FALSE;
     }
     return $this->libraryDefinitions[$library_name];