Cannot leave MAIL_USERNAME and MAIL_PASSWORD unset

[misilot]

Hello,

It is very common that you don't need to authenticate to your mail server when using a smart/relay host setup.
However, when I try to leave them unset I get the following error.

MAIL_USERNAME
none is not an allowed value (type=type_error.none.not_allowed)
MAIL_PASSWORD
none is not an allowed value (type=type_error.none.not_allowed)

You can set them to an empty string and use USE_CREDENTIALS = false