Fix error when routing with array containing symbol.

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Bug Fixes
 
 * Use filter label when condition has a predicate. [#5886] by [@ko-lem]
+* Fix error when routing with array containing symbol. [#5870] by [@jwesorick]
 
 ### Removals
 

lib/active_admin/resource_controller/polymorphic_routes.rb

@@ -25,7 +25,7 @@ def to_named_resource(record)
           return ActiveAdmin::Model.new(active_admin_config, record)
         end
 
-        if record.is_a?(parent.class)
+        if respond_to?(:parent, true) && record.is_a?(parent.class)
           return ActiveAdmin::Model.new(active_admin_config.belongs_to_config.resource, record)
         end
 

spec/unit/resource_controller/polymorphic_routes_spec.rb

@@ -0,0 +1,30 @@
+require 'rails_helper'
+
+RSpec.describe ActiveAdmin::ResourceController::PolymorphicRoutes, type: :controller do
+  let(:klass) { Admin::PostsController }
+
+  shared_context 'with post config' do
+    before do
+      load_resources { post_config }
+
+      @controller = klass.new
+
+      get :index
+    end
+  end
+
+  context 'polymorphic routes' do
+    include_context 'with post config' do
+      let(:post_config) { ActiveAdmin.register Post }
+      let(:post) { Post.create! title: "Hello World" }
+    end
+
+    %w(polymorphic_url polymorphic_path).each do |method|
+      describe method do
+        it 'arrays wtih action names' do
+          expect(controller.send(method, [:admin, post])).to include("/admin/posts/#{post.id}")
+        end
+      end
+    end
+  end
+end