diff --git a/core/modules/outside_in/src/OffCanvasFormDialogTrait.php b/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
index e29e8bb6b2..e265a8cb1c 100644
--- a/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
+++ b/core/modules/outside_in/src/OffCanvasFormDialogTrait.php
@@ -18,7 +18,7 @@
 trait OffCanvasFormDialogTrait {
 
   /**
-   * Is the current request for an AJAX modal dialog.
+   * Determines if the current request is for an AJAX modal dialog.
    *
    * @return bool
    *   TRUE is the current request if for an AJAX modal dialog.
@@ -26,15 +26,15 @@
   protected function isModalDialog() {
     $wrapper_format = $this->getRequest()
       ->get(MainContentViewSubscriber::WRAPPER_FORMAT);
-    return (in_array($wrapper_format, [
+    return in_array($wrapper_format, [
       'drupal_ajax',
       'drupal_modal',
       'drupal_dialog_off_canvas',
-    ])) ? TRUE : FALSE;
+    ]);
   }
 
   /**
-   * Add modal dialog support to a form.
+   * Adds modal dialog support to a form.
    *
    * @param array $form
    *   An associative array containing the structure of the form.
@@ -99,18 +99,17 @@ public function submitFormDialog(array &$form, FormStateInterface $form_state) {
         '#type' => 'status_messages',
         '#weight' => -1000,
       ];
-      $response->addCommand(new HtmlCommand('#off-canvas-form', $form));
+      $command = new HtmlCommand('#off-canvas-form', $form);
     }
     else {
       if ($redirect_url = $this->getRedirectUrl()) {
-        $response->addCommand(new RedirectCommand($redirect_url->setAbsolute()
-          ->toString()));
+        $command = new RedirectCommand($redirect_url->setAbsolute()->toString());
       }
       else {
-        $response->addCommand(new CloseDialogCommand('#drupal-off-canvas'));
+        return $this->closeDialog($form, $form_state);
       }
     }
-    return $response;
+    return $response->addCommand($command);
   }
 
   /**
@@ -125,9 +124,7 @@ public function submitFormDialog(array &$form, FormStateInterface $form_state) {
    *   An AJAX response that display validation error messages.
    */
   public function closeDialog(array &$form, FormStateInterface $form_state) {
-    $response = new AjaxResponse();
-    $response->addCommand(new CloseDialogCommand('#drupal-off-canvas'));
-    return $response;
+    return (new AjaxResponse())->addCommand(new CloseDialogCommand('#drupal-off-canvas'));
   }
 
   /**
@@ -167,8 +164,6 @@ protected function getDestinationUrl() {
     if ($destination = $this->getRedirectDestinationPath()) {
       return Url::fromUserInput('/' . $destination);
     }
-
-    return NULL;
   }
 
   /**
@@ -181,7 +176,6 @@ protected function getRedirectDestinationPath() {
     if ($this->requestStack->getCurrentRequest()->get('destination')) {
       return $this->getRedirectDestination()->get();
     }
-    return NULL;
   }
 
   /**
diff --git a/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php b/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php
index b03ab22c0e..2c447fab64 100644
--- a/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php
+++ b/core/modules/outside_in/src/Render/MainContent/OffCanvasRender.php
@@ -42,13 +42,11 @@ public function renderResponse(array $main_content, Request $request, RouteMatch
     $response = new AjaxResponse();
 
     // Add place holder form messages from Ajax form requests.
-    $main_content = [
-      'off_canvas_messages' => [
-        '#type' => 'container',
-        '#attributes' => ['class' => ['messages__wrapper']],
-        '#weight' => 100,
-      ],
-    ] + $main_content;
+    $main_content['off_canvas_messages'] = [
+      '#type' => 'container',
+      '#attributes' => ['class' => ['messages__wrapper']],
+      '#weight' => 100,
+    ];
 
     // First render the main content, because it might provide a title.
     $content = $this->renderer->renderRoot($main_content);
diff --git a/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php b/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php
index 0e40595054..e561e9f595 100644
--- a/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php
+++ b/core/modules/outside_in/tests/modules/off_canvas_test/src/Form/TestForm.php
@@ -55,12 +55,7 @@ public function validateForm(array &$form, FormStateInterface $form_state) {
   }
 
   /**
-   * Form submission handler.
-   *
-   * @param array $form
-   *   An associative array containing the structure of the form.
-   * @param \Drupal\Core\Form\FormStateInterface $form_state
-   *   The current state of the form.
+   * {@inheritdoc}
    */
   public function submitForm(array &$form, FormStateInterface $form_state) {
     drupal_set_message('submitted');
diff --git a/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php b/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php
index 12b979dbc5..5c2facb6dd 100644
--- a/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php
+++ b/core/modules/outside_in/tests/src/FunctionalJavascript/OffCanvasTest.php
@@ -121,7 +121,7 @@ protected function getTestThemes() {
   }
 
   /**
-   * Test form errors in the Off-Canvas dialog.
+   * Tests form errors in the Off-Canvas dialog.
    */
   public function testFormErrors() {
     $web_assert = $this->assertSession();
diff --git a/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInJavascriptTestBase.php b/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInJavascriptTestBase.php
index ea2fe948fb..129aaec7ec 100644
--- a/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInJavascriptTestBase.php
+++ b/core/modules/outside_in/tests/src/FunctionalJavascript/OutsideInJavascriptTestBase.php
@@ -141,7 +141,7 @@ protected function getTestThemes() {
   }
 
   /**
-   * Assert the specified selector is visible after a wait.
+   * Asserts the specified selector is visible after a wait.
    *
    * @param string $selector
    *   The selector engine name. See ElementInterface::findAll() for the