having trouble with getting started and showing a window

I'm interested in lgi, and started following the overview, but none of these:

window.title = 'I am a window'
window:show_all()
window.title = window.title .. ' made by Lgi'

do anything and i get an error when i try window.has_resize_grip = true or print(window.style.resize_grip_height)

test.lua:

local lgi = require("lgi")

local Gtk = lgi.Gtk
local Gio = lgi.Gio
local GLib = lgi.GLib

local window = Gtk.Window()

window.title = "I am a window"
window:show_all()
window.title = window.title .. " made by Lgi"

window.has_resize_grip = true
print(window.style.resize_grip_height)

output:

~/coding/lgi_test » lua5.1 test.lua                                                                                                                                             mark@coollaptop
lua5.1: /usr/share/lua/5.1/lgi/override/Gtk.lua:87: bad argument #1 to 'format' (string expected, got nil)
stack traceback:
	[C]: in function 'format'
	/usr/share/lua/5.1/lgi/override/Gtk.lua:87: in function </usr/share/lua/5.1/lgi/override/Gtk.lua:83>
	test.lua:14: in main chunk
	[C]: ?

Start with docs/overview.md and reproduce the example using the test.lua snippet. Then inspect /usr/share/lua/5.1/lgi/override/Gtk.lua around line 87 and compare the reported property access with the documented API. Done means the getting-started example has a clear, working outcome and the reported error is addressed or documented.