Issue #2910320 by murilohp, malik.kotob: Validating managed files should account for null triggering elements

core/modules/file/src/Element/ManagedFile.php

@@ -411,7 +411,8 @@ class ManagedFile extends FormElement {
    * Render API callback: Validates the managed_file element.
    */
   public static function validateManagedFile(&$element, FormStateInterface $form_state, &$complete_form) {
-    $clicked_button = end($form_state->getTriggeringElement()['#parents']);
+    $triggering_element = $form_state->getTriggeringElement();
+    $clicked_button = isset($triggering_element['#parents']) ? end($triggering_element['#parents']) : '';
     if ($clicked_button != 'remove_button' && !empty($element['fids']['#value'])) {
       $fids = $element['fids']['#value'];
       foreach ($fids as $fid) {

core/modules/file/tests/src/Kernel/ManagedFileTest.php

@@ -0,0 +1,57 @@
+<?php
+
+namespace Drupal\Tests\file\Kernel;
+
+use Drupal\Core\Form\FormInterface;
+use Drupal\Core\Form\FormState;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Managed file element test.
+ *
+ * @group file
+ *
+ * @see \Drupal\file\Element\ManagedFile
+ */
+class ManagedFileTest extends FileManagedUnitTestBase implements FormInterface {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'form_test_managed_file';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['managed_file'] = [
+      '#type' => 'managed_file',
+    ];
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {}
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {}
+
+  /**
+   * Tests that managed file elements can be programmatically submitted.
+   */
+  public function testManagedFileElement() {
+    $form_state = new FormState();
+    $values['managed_file'] = NULL;
+    $form_state->setValues($values);
+    $this->container->get('form_builder')->submitForm($this, $form_state);
+    // Should submit without any errors.
+    $this->assertEquals(0, count($form_state->getErrors()));
+  }
+
+}