As found by n18fuhtm AT tutanota.com there are dhcp servers that send a

As found by n18fuhtm AT tutanota.com there are dhcp servers that send a
domain name option with length 1 and a single \0.
We strip trailing \0 and then end up with length 0.
This is a protocol violation, the minimum length for domain name option
is 1, and we ignore the lease.

Since we are not going to get this fixed this server side, we might as
well just pretend that we didn't receive a domain name (or host name).
We only ever care about them in the installer anyway. Not getting a
lease because of this corner case is not helpful.

OK deraadt