How to unset Mail-setting when creating new acme-issuer

Thank you for your library, it helped us a lot.

What is your question?

We are integrated certmagic as library to allow customers to work with their CAs but at the moment the email setting for the AcmeIssuer gets reused when setting it to an empty string, is this intentional? And if yes, how can we deactivate it?

What have you already tried?

setting the Email attribute to empty string as in:

magicConfig := certmagic.New(cache, *customConfig)

customIssuer := certmagic.ACMEIssuer{
	Agreed:               true,
	Email:                "",
	CA:                   config.AcmeServer,
	CertObtainTimeout:    20 * time.Second,
	DisableHTTPChallenge: true,
}

magicConfig.Issuers = []certmagic.Issuer{certmagic.NewACMEIssuer(magic, customIssuer)}
magicConfig.ManageSync(ctx, []string{Hostname})

Include any other information or discussion.

certmagic v0.20.0 but we are okay with upgrading, I just didn't find anything usefule for this problem in the changelog.

Bonus: What do you use this package for, and does it help you?

As a library to allow users to set their own certificates.

Start by tracing certmagic.NewACMEIssuer and how ACMEIssuer.Email is handled in the current version; the issue provides a reproducible configuration using an empty Email value. Check whether the existing behavior is intentional and how email can be disabled. Done means the behavior or supported configuration is clarified, with the issue's empty-string case addressed.