Don't use Rack::Sendfile middleware if x_sendfile_header is not present

railties/lib/rails/application.rb

@@ -163,7 +163,9 @@ def default_middleware_stack
         middleware.use ::Rails::Rack::Logger # must come after Rack::MethodOverride to properly log overridden methods
         middleware.use ::ActionDispatch::ShowExceptions, config.consider_all_requests_local
         middleware.use ::ActionDispatch::RemoteIp, config.action_dispatch.ip_spoofing_check, config.action_dispatch.trusted_proxies
-        middleware.use ::Rack::Sendfile, config.action_dispatch.x_sendfile_header
+        if config.action_dispatch.x_sendfile_header.present?
+          middleware.use ::Rack::Sendfile, config.action_dispatch.x_sendfile_header
+        end
         middleware.use ::ActionDispatch::Reloader unless config.cache_classes
         middleware.use ::ActionDispatch::Callbacks
         middleware.use ::ActionDispatch::Cookies