diff -u b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
--- b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
+++ b/core/lib/Drupal/Core/Config/ExtensionInstallStorage.php
@@ -93,14 +93,18 @@
         $module_list_scan = $listing->scan('module');
         $module_list = array();
         foreach (array_keys($modules) as $module) {
-          $module_list[$module] = $module_list_scan[$module];
+          if (isset($module_list_scan[$module])) {
+            $module_list[$module] = $module_list_scan[$module];
+          }
         }
         $this->folders += $this->getComponentNames($module_list);
       }
       if (!empty($extensions['theme'])) {
         $theme_list_scan = $listing->scan('theme');
         foreach (array_keys($extensions['theme']) as $theme) {
-          $theme_list[$theme] = $theme_list_scan[$theme];
+          if (isset($theme_list_scan[$theme])) {
+            $theme_list[$theme] = $theme_list_scan[$theme];
+          }
         }
         $this->folders += $this->getComponentNames($theme_list);
       }
@@ -112,8 +116,10 @@
         $profile = drupal_get_profile();
         if (isset($profile)) {
           $profile_list = $listing->scan('profile');
-          $profile_folders = $this->getComponentNames(array($profile_list[$profile]));
-          $this->folders = $profile_folders + $this->folders;
+          if (isset($profile_list[$profile])) {
+            $profile_folders = $this->getComponentNames(array($profile_list[$profile]));
+            $this->folders = $profile_folders + $this->folders;
+          }
         }
       }
     }
diff -u b/core/lib/Drupal/Core/Config/InstallStorage.php b/core/lib/Drupal/Core/Config/InstallStorage.php
--- b/core/lib/Drupal/Core/Config/InstallStorage.php
+++ b/core/lib/Drupal/Core/Config/InstallStorage.php
@@ -162,7 +162,9 @@
       $listing = new ExtensionDiscovery(DRUPAL_ROOT);
       if ($profile = drupal_get_profile()) {
         $profile_list = $listing->scan('profile');
-        $this->folders += $this->getComponentNames(array($profile_list[$profile]));
+        if (isset($profile_list[$profile])) {
+          $this->folders += $this->getComponentNames(array($profile_list[$profile]));
+        }
       }
       $this->folders += $this->getComponentNames($listing->scan('module'));
       $this->folders += $this->getComponentNames($listing->scan('theme'));
diff -u b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
--- b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
+++ b/core/lib/Drupal/Core/Extension/ExtensionDiscovery.php
@@ -125,9 +125,8 @@
    */
   public function scan($type, $include_tests = NULL) {
     // Determine the installation profile directories to scan for extensions,
-    // unless explicit profile directories have been set. Exclude profiles
-    // as we can't have profiles within profiles.
-    if (!isset($this->profileDirectories) && $type != 'profile') {
+    // unless explicit profile directories have been set.
+    if (!isset($this->profileDirectories)) {
       $this->setProfileDirectoriesFromSettings();
     }
 
@@ -135,8 +134,9 @@
    */
   public function scan($type, $include_tests = NULL) {
     // Determine the installation profile directories to scan for extensions,
-    // unless explicit profile directories have been set.
-    if (!isset($this->profileDirectories)) {
+    // unless explicit profile directories have been set. Exclude profiles
+    // as we can't have profiles within profiles.
+    if (!isset($this->profileDirectories) && $type != 'profile') {
       $this->setProfileDirectoriesFromSettings();
     }
 
diff -u b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
--- b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
+++ b/core/modules/system/src/Tests/Bootstrap/GetFilenameUnitTest.php
@@ -17,13 +17,6 @@
 class GetFilenameUnitTest extends KernelTestBase {
 
   /**
-   * The container used by the test, moved out of the way.
-   *
-   * @var \Symfony\Component\DependencyInjection\ContainerInterface
-   */
-  protected $previousContainer;
-
-  /**
    * Tests that drupal_get_filename() works when the file is not in database.
    */
   function testDrupalGetFilename() {