diff -u b/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php b/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php
--- b/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ModuleStream.php
@@ -35,6 +35,8 @@
 
   /**
    * Wraps the ModuleHandler service.
+   *
+   * @return \Drupal\Core\Extension\ModuleHandlerInterface
    */
   protected function moduleHandler() {
     return \Drupal::moduleHandler();
diff -u b/core/lib/Drupal/Core/StreamWrapper/SystemStream.php b/core/lib/Drupal/Core/StreamWrapper/SystemStream.php
--- b/core/lib/Drupal/Core/StreamWrapper/SystemStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/SystemStream.php
@@ -80,6 +80,8 @@
 
   /**
    * Wraps the drupal request.
+   *
+   * @return \Symfony\Component\HttpFoundation\Request
    */
   protected function request() {
     return \Drupal::request();
diff -u b/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php b/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php
--- b/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php
+++ b/core/lib/Drupal/Core/StreamWrapper/ThemeStream.php
@@ -47,6 +47,8 @@
 
   /**
    * Gets the currently active theme.
+   *
+   * @return mixed
    */
   protected function getActiveTheme() {
     return \Drupal::service('theme.negotiator')->determineActiveTheme(\Drupal::service('current_route_match'));
@@ -63,6 +65,9 @@
 
   /**
    * Wraps the drupal configuration service.
+   *
+   * @param $config_name
+   * @return \Drupal\Core\Config\Config
    */
   protected function config($config_name) {
     return \Drupal::config($config_name);