AC railtie should configure helpers path.

actionpack/lib/action_controller/metal/helpers.rb

@@ -50,9 +50,8 @@ module ActionController
     include AbstractController::Helpers
 
     included do
-      extlib_inheritable_accessor(:helpers_path) do
-        defined?(Rails::Application) ? Rails::Application.paths.app.helpers.to_a : []
-      end
+      extlib_inheritable_accessor(:helpers_path)
+      self.helpers_path = []
     end
 
     module ClassMethods

actionpack/lib/action_controller/railtie.rb

@@ -21,5 +21,9 @@ module ActionController
     initializer "action_controller.initialize_framework_caches" do
       ActionController::Base.cache_store ||= RAILS_CACHE
     end
+
+    initializer "action_controller.set_helpers_path" do |app|
+      ActionController::Base.helpers_path = app.config.paths.app.helpers.to_a
+    end
   end
 end

activesupport/lib/active_support/railtie.rb

@@ -7,13 +7,13 @@ module ActiveSupport
 
     # Loads support for "whiny nil" (noisy warnings when methods are invoked
     # on +nil+ values) if Configuration#whiny_nils is true.
-    initializer :initialize_whiny_nils do |app|
+    initializer "active_support.initialize_whiny_nils" do |app|
       require 'active_support/whiny_nil' if app.config.whiny_nils
     end
 
     # Sets the default value for Time.zone
     # If assigned value cannot be matched to a TimeZone, an exception will be raised.
-    initializer :initialize_time_zone do |app|
+    initializer "active_support.initialize_time_zone" do |app|
       require 'active_support/core_ext/time/zones'
       zone_default = Time.__send__(:get_zone, app.config.time_zone)
 
@@ -36,7 +36,7 @@ module I18n
     config.i18n.engines_load_path = []
     config.i18n.load_path = []
 
-    initializer :initialize_i18n do
+    initializer "i18n.initialize" do
       require 'active_support/i18n'
 
       ActionDispatch::Callbacks.to_prepare do