Log in as admin

"manage jenkins"

"manage users"

"Create user"

add a username with a dot "hans.muster", fill all other fields

click on "create user" -> nothing happens

-> better to show the same warning as when a user can sign up:

"Username - User name must only contain alphanumeric characters, underscore and dash"

Further problem: when a user is auto-detected (after a commit) a dot is allowed, and in our case wanted.

-> perhabs it  is better to allow dots