Issue #3020718 by jibran, Sam152: system_post_update_add_expand_all_items_key_in_system_menu_block fails if blocks module is disabled

core/modules/system/system.post_update.php

@@ -183,6 +183,9 @@ function system_post_update_states_clear_cache() {
  * Initialize 'expand_all_items' values to system_menu_block.
  */
 function system_post_update_add_expand_all_items_key_in_system_menu_block(&$sandbox = NULL) {
+  if (!\Drupal::moduleHandler()->moduleExists('block')) {
+    return;
+  }
   \Drupal::classResolver(ConfigEntityUpdater::class)->update($sandbox, 'block', function ($block) {
     return strpos($block->getPluginId(), 'system_menu_block:') === 0;
   });

core/modules/system/tests/src/Functional/Update/NoDependenciesUpdateTest.php

@@ -0,0 +1,36 @@
+<?php
+
+namespace Drupal\Tests\system\Functional\Update;
+
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * Test the system module updates with no dependencies installed.
+ *
+ * @group Update
+ * @group legacy
+ */
+class NoDependenciesUpdateTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $installProfile = 'testing';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../tests/fixtures/update/drupal-8.6.0.bare.testing.php.gz',
+    ];
+  }
+
+  /**
+   * Test the system module updates with no dependencies installed.
+   */
+  public function testNoDependenciesUpdate() {
+    $this->runUpdates();
+  }
+
+}