AppIndicator3 demo

I tried to make a demo application that uses AppIndicator3 library. That's what I got so far:

local lgi = require 'lgi'

local GLib, Gtk, Gdk, Gio, GObject = lgi.GLib, lgi.Gtk, lgi.Gdk, lgi.Gio, lgi.GObject
local AppIndicator = lgi.AppIndicator3

local app = Gio.Application { application_id = 'org.lgi.appindicator3' }

local menu = Gtk.Menu()

menu:append(
	Gtk.MenuItem {
		label = 'Exit';
		on_activate = function() app:release() end;
		sensitive = true;
	}
)

function app:on_activate()
	local ind = AppIndicator.Indicator.new(app.application_id, 'gtk-info', 'SYSTEM_SERVICES')
	ind:set_menu(menu)
	ind:set_status('ACTIVE')
	app:hold()
end

app:run({arg[0], ...})

I expect it to show icon with single drop-down option "Exit". What I get, however, is icon with empty menu (no Exit option).

What could be a problem here? If it matters, I'm using cinnamon with indicators support turned on.

Start with the demo's app:on_activate entry point and the AppIndicator.Indicator.new and set_menu calls. Reproduce the empty menu under Cinnamon with indicator support enabled, then trace why the appended Gtk.MenuItem is not displayed; done when the indicator shows the Exit option.