PHP表单验证通过，即使存在错误

我正在尝试开发一个表单验证系统。但问题是，即使用户没有按照要求提供数据，验证也会通过。不知道问题出在哪里。

这是我的表单验证类

 class Validation
 {
private $_passed = false,
        $_errors = array(),
        $_db = null;
public function __construct() {
        $this->_db = DB::getInstance();
    }
public function check($source, $items= array()) {
        foreach ($items as $item => $rules) {
            foreach ($rules as $rule => $rule_value) {
                $value = $source[$item];
                if ($rule === 'required' && empty($value)) {
                    $this->addError("{$item} is required");
                } else {
                }
            }
        }
        if (empty($this->_errors)) {
            $this->_passed = true;
        }
        return $this;
    }
private function addError($error) {
        $this->errors[] = $error;
    }
public function errors() {
        return $this->_errors;
    }
public function passed() {
        return $this->_passed;
    }
 }

这是包含Html表单的表单页面。

require_once 'core/init.php';
if (Input::exists()) {
    $validate = new Validation();
    $validation = $validate->check($_POST, array(
        'username' => array(
            'required' => true,
            'min' => 2,
            'max' => 20,
            'unique' => 'users'
            ),
        'password' => array(
            'required' => true,
            'matches' => 'password'
            ),
        'password_again' => array(
            'required' => true,
            'min' => 6
            ),
        'name' => array(
            'required' => true,
            'min' => 2,
            'max' => 60
            ),
        ));
    if ($validation->passed()) {
        //register new user
        echo "passed"; //this passes even though users provides no data
    } else {
        print_r($validation->errors());
    }
}

因此，即使用户根本没有提供任何数据，我得到的只是屏幕上传递的echo。它应该抛出错误。请帮忙。感谢