In my 1.1.8 deployment the system domain-name statement allowed a domain name ending in a dot (i.e. thus "rooted"), like for example something. (i.e. with a dot . after something.)
However after upgrading to 1.2.0 201904151631 the system fails to properly configure the system name (including the host-name statement). However manually re-configuring the domain-name, it gives a warning about the extra dot.
I would say that the domain-name statement should allow domain names ending in a dot, or if it is considered forbidden, then the migration script should trim that character upon migration.
(I've originally posted this issue on the public forum: https://forum.vyos.io/t/issues-encountered-while-upgrading-from-1-1-8-to-1-2-0-201904151631/3635)