Issue #3104980 by danflanagan8, acbramley:...

Issue #3104980 by danflanagan8, acbramley: layout_builder_system_breadcrumb_alter doesn't check for a null route object

core/modules/layout_builder/layout_builder.module

@@ -334,7 +334,7 @@ function layout_builder_plugin_filter_layout_alter(array &$definitions, array $e
  */
 function layout_builder_system_breadcrumb_alter(Breadcrumb &$breadcrumb, RouteMatchInterface $route_match, array $context) {
   // Remove the extra 'Manage display' breadcrumb for Layout Builder defaults.
-  if ($route_match->getRouteObject()->hasOption('_layout_builder') && $route_match->getParameter('section_storage_type') === 'defaults') {
+  if ($route_match->getRouteObject() && $route_match->getRouteObject()->hasOption('_layout_builder') && $route_match->getParameter('section_storage_type') === 'defaults') {
     $links = array_filter($breadcrumb->getLinks(), function (Link $link) use ($route_match) {
       $entity_type_id = $route_match->getParameter('entity_type_id');
       if (!$link->getUrl()->isRouted()) {

core/modules/layout_builder/tests/src/Kernel/LayoutBuilderBreadcrumbAlterTest.php

+<?php
+
+namespace Drupal\Tests\layout_builder\Kernel;
+
+use Drupal\Core\Breadcrumb\Breadcrumb;
+use Drupal\Core\Routing\NullRouteMatch;
+use Drupal\KernelTests\Core\Entity\EntityKernelTestBase;
+
+/**
+ * Tests layout_builder_system_breadcrumb_alter().
+ *
+ * @group layout_builder
+ */
+class LayoutBuilderBreadcrumbAlterTest extends EntityKernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'layout_builder',
+    'layout_discovery',
+  ];
+
+  /**
+   * Check that there are no errors when alter called with null route match.
+   */
+  public function testBreadcrumbAlterNullRouteMatch() {
+    $breadcrumb = new Breadcrumb();
+    $route_match = new NullRouteMatch();
+    layout_builder_system_breadcrumb_alter($breadcrumb, $route_match, []);
+  }
+
+}