Model 里的 $dispather 属性,是如何在实例化之前就有 默认值了？没有看到在哪里去设置这个值的

我在 Illuminate\Database\Eloquent\Model 里 var_dump(static::$dispatcher)

 public function __construct(array $attributes = [])
    {
        var_dump(static::$dispatcher);
        $this->bootIfNotBooted();

        $this->syncOriginal();

        $this->fill($attributes);
    }

构造函数并没有去设置 $dispatcher 这个值

但在页面上可以得到这个值

/home/vagrant/Code/blog/vendor/laravel/framework/src/Illuminate/Database/Eloquent/Model.php:152:
object(Illuminate\Events\Dispatcher)[23]
  protected 'container' => 
    object(Illuminate\Foundation\Application)[3]
      protected 'basePath' => string '/home/vagrant/Code/blog' (length=23)
      protected 'hasBeenBootstrapped' => boolean true
      protected 'booted' => boolean false
      protected 'bootingCallbacks' => 
        array (size=2)
          0 => 
            object(Closure)[158]
              ...
          1 => 
            object(Closure)[180]
              ...
      protected 'bootedCallbacks' => 
        array (size=1)
          0 => 
            object(Closure)[123]

请问这个值是在哪一步给设置进去了