diff --git a/core/lib/Drupal/Core/DrupalKernel.php b/core/lib/Drupal/Core/DrupalKernel.php
index 08cf959..193ab8f 100644
--- a/core/lib/Drupal/Core/DrupalKernel.php
+++ b/core/lib/Drupal/Core/DrupalKernel.php
@@ -520,19 +520,19 @@ protected function initializeContainer() {
     if (isset($this->container)) {
       // All namespaces must be registered before we attempt to use any service
       // from the container.
+      $container_modules = (array) $this->container->getParameter('container.modules');
+      $container_themes = (array) $this->container->getParameter('container.themes');
       $namespaces_before = $this->classLoader->getPrefixes();
-      $container_modules = $this->container->getParameter('container.modules');
       $this->registerNamespaces($this->getNamespaces($container_modules));
-      $container_themes = $this->container->getParameter('container.themes');
       $this->registerNamespaces($this->getNamespaces($container_themes));

       // If 'container.modules' or 'container.themes' is wrong, the container
       // must be rebuilt.
       if (!isset($this->moduleList)) {
-        $this->moduleList = $this->container->get('config.factory')->get('system.module')->load()->get('enabled');
+        $this->moduleList = (array) $this->container->get('config.factory')->get('system.module')->load()->get('enabled');
       }
       if (!isset($this->themeList)) {
-        $this->themeList = $this->container->get('config.factory')->get('system.theme')->load()->get('enabled');
+        $this->themeList = (array) $this->container->get('config.factory')->get('system.theme')->load()->get('enabled');
       }
       if (array_keys($this->moduleList) !== array_keys($container_modules) || array_keys($this->themeList) !== array_keys($container_themes)) {
         $persist = $this->getServicesToPersist();
@@ -618,7 +618,7 @@ protected function buildContainer() {
     $container->setParameter('container.themes', $this->getThemeFileNames());

     // Get a list of namespaces and put it onto the container.
-    $namespaces = $this->getNamespaces(array_merge_recursive($this->getModuleFileNames(), $this->getThemeFileNames()));
+    $namespaces = $this->getNamespaces(array_merge($this->getModuleFileNames(), $this->getThemeFileNames()));

     // Add all components in \Drupal\Core and \Drupal\Component that have a
     // Plugin directory.