Issue #2475805 by tstoeckler, googletorp, webwarrior:...

Issue #2475805 by tstoeckler, googletorp, webwarrior: menu_ui_form_node_form_submit() is called when the Preview button is pressed which fatals

core/modules/menu_ui/menu_ui.module

@@ -334,7 +334,7 @@ function menu_ui_form_node_form_alter(&$form, FormStateInterface $form_state) {
   );
 
   foreach (array_keys($form['actions']) as $action) {
-    if (isset($form['actions'][$action]['#type']) && $form['actions'][$action]['#type'] === 'submit') {
+    if ($action != 'preview' && isset($form['actions'][$action]['#type']) && $form['actions'][$action]['#type'] === 'submit') {
       $form['actions'][$action]['#submit'][] = 'menu_ui_form_node_form_submit';
     }
   }

core/modules/menu_ui/src/Tests/MenuNodeTest.php

@@ -91,6 +91,14 @@ function testMenuNodeFormWidget() {
     $this->drupalPostForm('admin/structure/types/manage/page', $edit, t('Save content type'));
     $this->assertRaw(t('The content type %name has been updated.', array('%name' => 'Basic page')));
 
+    // Test that we can preview a node that will create a menu item.
+    $edit = array(
+      'title[0][value]' => $node_title,
+      'menu[enabled]' => 1,
+      'menu[title]' => 'Test preview',
+    );
+    $this->drupalPostForm('node/add/page', $edit, t('Preview'));
+
     // Create a node.
     $node_title = $this->randomMachineName();
     $edit = array(