Issue #2604220 by yched, swentel, Cottser: PHP notice for single value image field configured with a default image (no image present) and a hidden label

core/includes/theme.inc

@@ -1535,7 +1535,7 @@ function template_preprocess_field(&$variables, $hook) {
   }
 
   // Merge attributes when a single-value field has a hidden label.
-  if ($element['#label_display'] == 'hidden' && !$variables['multiple']) {
+  if ($element['#label_display'] == 'hidden' && !$variables['multiple'] && !empty($element['#items'][0]->_attributes)) {
     $variables['attributes'] = NestedArray::mergeDeep($variables['attributes'], (array) $element['#items'][0]->_attributes);
   }
 

core/modules/image/src/Tests/ImageFieldDefaultImagesTest.php

@@ -7,6 +7,7 @@
 
 namespace Drupal\image\Tests;
 use Drupal\Component\Utility\Unicode;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
 use Drupal\file\Entity\File;
 
 /**
@@ -162,6 +163,13 @@ class ImageFieldDefaultImagesTest extends ImageFieldTestBase {
       )
     );
 
+    // Also check that the field renders without warnings when the label is
+    // hidden.
+    EntityViewDisplay::load('node.article.default')
+      ->setComponent($field_name, array('label' => 'hidden', 'type' => 'image'))
+      ->save();
+    $this->drupalGet('node/' . $article->id());
+
     // Confirm that the image default is shown for a new page node.
     $page = $this->drupalCreateNode(array('type' => 'page'));
     $page_built = $this->drupalBuildEntityView($page);