I want sudo to behave like this, for all users:
If the user currently has a non-empty password, prompt for the password.
If the user currently has an empty password, either prompt for the password and accept the empty string, or don't prompt at all and permit.
Is this possible? Right now, I have (1) but this is what happens for a user with an empty password:
$ sudo echo Sorry, try again. Sorry, try again. Sorry, try again. sudo: 3 incorrect password attempts
Alternatively, I can switch off password checking per-user, but that's not what I want, because the user might set a password later, and then sudo should prompt for it.