Issue #3273497: Passing null to parameter #1 ($data) of type string to unserialize() is deprecated

Closes #3273497

src/Plugin/Field/FieldFormatter/ViewsReferenceFieldFormatter.php

@@ -88,7 +88,7 @@ class ViewsReferenceFieldFormatter extends FormatterBase implements TrustedCallb
           [
             $view_name,
             $display_id,
-            $item->getValue()['data'],
+            $item->getValue()['data'] ?? '',
             serialize($enabled_settings),
             !empty(array_filter($this->getSetting('plugin_types'))),
           ],
@@ -121,8 +121,8 @@ class ViewsReferenceFieldFormatter extends FormatterBase implements TrustedCallb
    *   Whether plugin types were enabled.
    */
   public static function lazyBuilder(string $view_name, string $display_id, string $data, string $enabled_settings, bool $plugin_types): array {
-    $data = unserialize($data, ['allowed_classes' => FALSE]);
-    $enabled_settings = unserialize($enabled_settings, ['allowed_classes' => FALSE]);
+    $unserialized_data = !empty($data) ? unserialize($data, ['allowed_classes' => FALSE]) : [];
+    $unserialized_enabled_settings = !empty($enabled_settings) ? unserialize($enabled_settings, ['allowed_classes' => FALSE]) : [];
     $view = Views::getView($view_name);
 
     // Add an extra check because the view could have been deleted.
@@ -136,8 +136,8 @@ class ViewsReferenceFieldFormatter extends FormatterBase implements TrustedCallb
     // behaviour in views. The hook_views_pre_build() needs to know if the
     // view was part of a viewsreference field or not.
     $view->element['#viewsreference'] = [
-      'data' => $data,
-      'enabled_settings' => $enabled_settings,
+      'data' => $unserialized_data,
+      'enabled_settings' => $unserialized_enabled_settings,
     ];
 
     $view->preExecute();