JENKINS-43736 introduced functionality to update the user's email address using SAML. I'm having trouble getting this to work.

I have done the following:

1. Verified that my SAML assertion contains an attribute with the name "uid".
2. Set the "Email Attribute" field to "uid" through the UI.
3. Logged in to Jenkins using SAML.
4. Confirmed that my user's config.xml does not include the contents of the "uid" attribute in my SAML assertion.

I believe part of the problem may be this line: https://github.com/jenkinsci/saml-plugin/blob/master/src/main/java/org/jenkinsci/plugins/saml/SamlSecurityRealm.java#L343

From the code, it looks as though a user without an email currently set will not have their email updated by the SAML plugin. When I tried logging out, manually modifying my user's config to contain a non-null value, then logging back in I found that my config was updated to contain a null value again.

Happy to help debug further.