cakephp-4.x - CakePHP4 - 如何在另一个组件中使用“RequestHandler”组件

Question

我的组件的 PHP 代码段如下所示：

...
class NewsletterFormComponent extends Component {

public $components = ['Flash','RequestHandler'];
public $controller;


public function beforeFilter()
{
$this->controller = $this->getController();
}

public function registration($data = null) {
...
if ($this->request->is('post')) {
//do something
}
...
}
...

显示如下错误：
Call to a member function is() on null
如何解决这个问题？