findOne() 的问题 [ 2.0 版本 ]

public static function findByUsername($username)
{
    return static::findOne(['username'=>$username]);
}


public function getUser()
{
    if ($this->_user === false) {
        $this->_user = User::findByUsername($this->username);
        var_dump($this->_user);
    }
    return $this->_user;
}

代码如上：
var_dump出来的值如下：

  public 'id' => null
  public 'username' => null
  public 'password' => null
  public 'authKey' => null
  public 'accessToken' => null
  private '_attributes' (yii\db\BaseActiveRecord) => 
    array (size=5)
      'id' => int 1
      'username' => string 'hello' (length=5)
      'password' => string 'hello' (length=5)
      'auth_key' => null
      'accessToken' => null
  private '_oldAttributes' (yii\db\BaseActiveRecord) => 
    array (size=5)
      'id' => int 1
      'username' => string 'hello' (length=5)
      'password' => string 'hello' (length=5)
      'auth_key' => null
      'accessToken' => null
  private '_related' (yii\db\BaseActiveRecord) => 
    array (size=0)
      empty
  private '_errors' (yii\base\Model) => null
  private '_validators' (yii\base\Model) => null
  private '_scenario' (yii\base\Model) => string 'default' (length=7)
  private '_events' (yii\base\Component) => 
    array (size=0)
      empty
  private '_behaviors' (yii\base\Component) => 
    array (size=0)
      empty

疑问：findOne 出来的值，是否正确，我想取出 password 这个字段该怎么做？