Email User and Password

Hi!
Leaving SMTPUser and SMTPPasss empty on Email.php cause send() not to log user on smtp server when setting this on the fly.
I don't think it`s expected since these values are being passed through a user function
CI 4.4.3

PHP Code:

        $email->SMTPUser = getenv('mail.smtpUser');

        $email->SMTPPass = getenv('mail.smtpPass'); 


This code work if SMTPUser and SMTPPass is set to anything on Email.php.
Thanks.