Issue #3342489 by _shY, smustgrave, longwave, Wim Leers: Add default value for mail_notification in site.system config

core/modules/system/config/install/system.site.yml

@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 default_langcode: en
+mail_notification: null

core/modules/system/system.post_update.php

@@ -201,3 +201,14 @@ function system_post_update_amend_config_sync_readme_url() {
   file_put_contents($readme_path, $changed_content);
   return \t('Amended configuration synchronization readme file content.');
 }
+
+/**
+ * Adds default value for the mail_notification config parameter.
+ */
+function system_post_update_mail_notification_setting() {
+  $config = \Drupal::configFactory()->getEditable('system.site');
+  // If the value doesn't exist it always returns NULL.
+  if (is_null($config->get('mail_notification'))) {
+    $config->set('mail_notification', NULL)->save();
+  }
+}

core/modules/system/tests/src/Kernel/Migrate/d6/MigrateSystemConfigurationTest.php

@@ -109,6 +109,7 @@ class MigrateSystemConfigurationTest extends MigrateDrupal6TestBase {
       'admin_compact_mode' => FALSE,
       'weight_select_max' => 100,
       'default_langcode' => 'en',
+      'mail_notification' => NULL,
     ],
   ];
 

core/modules/system/tests/src/Kernel/Migrate/d7/MigrateSystemConfigurationTest.php

@@ -118,6 +118,7 @@ class MigrateSystemConfigurationTest extends MigrateDrupal7TestBase {
       'admin_compact_mode' => TRUE,
       'weight_select_max' => 100,
       'default_langcode' => 'en',
+      'mail_notification' => NULL,
     ],
   ];
 

core/profiles/demo_umami/config/install/system.site.yml

@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 default_langcode: en
+mail_notification: null

core/profiles/standard/config/install/system.site.yml

@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 100
 default_langcode: en
+mail_notification: null

core/profiles/testing_config_overrides/config/install/system.site.yml

@@ -10,3 +10,4 @@ page:
 admin_compact_mode: false
 weight_select_max: 91
 default_langcode: en
+mail_notification: null