Login cant validate password

i use login form from yii2 basic but i cant login
it says incorrect username or password
i use mysql for my db

public function getUser()
    if ($this->_user === true) {
        $this->_user = User::findByUsername($this->username);

    return $this->_user;

i have made change in that function, change user === false into true
because if it false the page cant load because an error