first commit

core/modules/contact/contact.post_update.php

@@ -0,0 +1,27 @@
+<?php
+
+/**
+ * @file
+ * Post update functions for Contact.
+ */
+
+/**
+ * Implements hook_removed_post_updates().
+ */
+function contact_removed_post_updates() {
+  return [
+    'contact_post_update_add_message_redirect_field_to_contact_form' => '9.0.0',
+  ];
+}
+
+/**
+ * Converts empty `default_form` in settings to NULL.
+ */
+function contact_post_update_set_empty_default_form_to_null(): void {
+  $config = \Drupal::configFactory()->getEditable('contact.settings');
+  // 'default_form' in 'contact.settings' config must be stored as NULL if it
+  // is empty.
+  if ($config->get('default_form') === '') {
+    $config->set('default_form', NULL)->save();
+  }
+}