User creation from LDAP with custom or server trusted authentication should never fail

For example, in my case, because of XWIKI-2577, user creation from LDAP with property xwiki.authentication.createuser can fail.
Built-in authenticators should consider to switch to empty creation of users because in those cases, this is field mapping and not related to authentication.
Maybe by adding a new property or considering multi valued property: "createuser,empty" in order to consider both one after another.