Issue #1618458 by Cottser, Jody Lynn, grndlvl: Fixed help_menu() creates unnecessary router items.

core/modules/help/help.module

@@ -16,15 +16,10 @@ function help_menu() {
     'weight' => 9,
   );
 
-  $modules = Drupal::moduleHandler()->getImplementations('help');
-  ksort($modules);
-  foreach ($modules as $module) {
-    $items['admin/help/' . $module] = array(
-      'title' => $module,
-      'route_name' => 'help_page',
-      'type' => MENU_VISIBLE_IN_BREADCRUMB,
-    );
-  }
+  $items['admin/help/%'] = array(
+    'route_name' => 'help_page',
+    'type' => MENU_VISIBLE_IN_BREADCRUMB,
+  );
 
   return $items;
 }

core/modules/help/lib/Drupal/help/Controller/HelpController.php

@@ -9,6 +9,7 @@
 use Drupal\Core\Controller\ControllerInterface;
 use Drupal\Core\Extension\ModuleHandlerInterface;
 use Symfony\Component\DependencyInjection\ContainerInterface;
+use Symfony\Component\HttpKernel\Exception\NotFoundHttpException;
 
 /**
  * Controller routines for help routes.
@@ -98,6 +99,8 @@ protected function helpLinksAsList() {
    *
    * @return array
    *   A render array as expected by drupal_render().
+   *
+   * @throws \Symfony\Component\HttpKernel\Exception\NotFoundHttpException
    */
   public function helpPage($name) {
     $build = array();
@@ -132,9 +135,11 @@ public function helpPage($name) {
           '#links' => $links,
         );
       }
+      return $build;
+    }
+    else {
+      throw new NotFoundHttpException();
     }
-
-    return $build;
   }
 
 }