diff --git a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
index 627e4fe..872dfc6 100644
--- a/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
@@ -165,9 +165,8 @@ public function __construct($root, $use_file_cache = TRUE, $profile_directories
   public function scan($type, $include_tests = NULL) {
     // Determine the installation profile directories to scan for extensions,
     // unless explicit profile directories have been set. Exclude profiles as we
-    // cannot have profiles within profiles. If no profiles are specified in the
-    // constructor, profileDirectories will be NULL.
-    if (($this->profileDirectories === NULL) && $type != 'profile') {
+    // cannot have profiles within profiles.
+    if (!isset($this->profileDirectories) && $type != 'profile') {
       $this->setProfileDirectoriesFromSettings();
     }