app:on_command_line() is broken

Attempting to use the app:on_command_line signal leads to a crash:

#!/usr/bin/env lua5.1
lgi = require('lgi')
local gtk = lgi.require('Gtk', '3.0')
local gio = lgi.require('Gio', '2.0')

local app = gtk.Application {
    flags = gio.ApplicationFlags.HANDLES_COMMAND_LINE,
}

function app:on_command_line(command) end

app:run { arg[0], ... } --method shown in the examples
--app:run(arg) --another method I thought might work

This script fails with:

lua5.1: /usr/share/lua/5.1/lgi/override/GObject-Value.lua:78: bad argument #3 to 'get' (number expected, got nil)
stack traceback:
    [C]: in function 'get'
    /usr/share/lua/5.1/lgi/override/GObject-Value.lua:78: in function 'marshaller'
    /usr/share/lua/5.1/lgi/override/GObject-Closure.lua:126: in function 'marshal_cell'
    /usr/share/lua/5.1/lgi/override/GObject-Closure.lua:162: in function </usr/share/lua/5.1/lgi/override/GObject-Closure.lua:144>
    [C]: in function 'run'
    ./gtk-test.lua:12: in main chunk
    [C]: ?

Run the provided gtk-test.lua reproduction with Lua 5.1 and inspect the failure through lgi/override/GObject-Value.lua and lgi/override/GObject-Closure.lua. Trace app:on_command_line during app:run and make the signal invocation complete without the reported marshalling crash.