public function existingIdentity($attribute, $params)
    {
        if ($this->hasErrors()) {
            return false;
        }
        $identity = $this->getIdentity();
        if ($identity === null) {
            if ($this->username !== null) {
                $this->addError('username', Yii::t('usr', 'No user found matching this username.'));
            } elseif ($this->email !== null) {
                $this->addError('email', Yii::t('usr', 'No user found matching this email address.'));
            } else {
                $this->addError('username', Yii::t('usr', 'Please specify username or email.'));
            }

            return false;
        } elseif ($identity->isDisabled()) {
            $this->addError('username', Yii::t('usr', 'User account has been disabled.'));

            return false;
        }

        return true;
    }