Class property gets null as a value - php

Question

I have two classes:
DI
namespace engine\DI;
class DI
{
/**
* #var array
*/
private $container = [];
/**
* #param $key
* #param $value
* #return $this
*/
public function set($key, $value)
{
$this->container[$key] = $value;
return $this;
}
/**
* #param $key
* #return mixed
*/
public function get($key)
{
return $this->has($key);
}
public function has($key)
{
return $this->container[$key] ?? null;
}
}
and Cms
namespace engine;
use engine\DI\DI;
class Cms
{
/**
* #var DI
*/
private $di;
public $router;
/**
* #param $di
*/
public function __construct($di)
{
$this->di = $di;
$this->router = $this->di->get('router');
}
/**
* #return void
*/
public function run()
{
//$this->router->add('home', '/', 'HomeController:index');
print_r($this->router);
}
}
As you can see in Cms, I put a $router's value in constructor and for some reason it remains null. The interesting part is when I print_r($this->di->get('router')) it works just fine and returns proper value. Even more, when I call method by this value directly (like $this->di->get('router')->add();) it also works wonders, so the value itself is clearly not null. What could be the reason of this?
Here are two additional files where the value comes from:
Provider:
namespace engine\service\router;
use engine\service\AbstractProvider;
use engine\core\router\Router;
class Provider extends AbstractProvider
{
public string $service_name = 'router';
/**
* #inheritDoc
*/
function init()
{
$router = new Router('cms/');
$this->di->set($this->service_name, $router);
}
Bootstrap:
use engine\Cms;
use engine\DI\DI;
try {
$di = new DI();
$cms = new Cms($di);
$services = require 'config/services.php'; //stores an array with providers
foreach ($services as $key => $service) {
$provider = new $service($di);
$provider->init();
}
$cms->run();
} catch (\ErrorException $e) {
echo $e->getMessage();
}

Answer 1

After adding the additional info, it seems like what Nigel Ren has pointed in the comments is in fact the issue.
You should have it like this:
try {
$di = new DI();
$services = require 'config/services.php'; //stores an array with providers
foreach ($services as $key => $service) {
$provider = new $service($di);
$provider->init();
}
$cms = new Cms($di); // creating the Cms object after di is initialized
$cms->run();
} catch (\ErrorException $e) {
echo $e->getMessage();
}

Answer 2

Have you tried something like that :
public function __construct($di)
{
$this->di = new $di();
$this->router = $this->di->get('router');
}

Answer 3

try {
$di = new DI();
$services = require 'config/services.php';
foreach ($services as $key => $service) {
$provider = new $service($di);
$provider->init();
}
$cms = new Cms($di);
$cms->run();
} catch (\ErrorException $e) {
echo $e->getMessage();
}