Confirm edit hosts functionality issue/bug

I think I have found a usability issue/bug: If one doesn't have a
puppet proxy setup, the "Puppet Master" field will be blank and won't
allow any input, but input validation barfs if you try to edit a host
and the puppet master field is left blank.

Is this the behavior others are seeing? (I am running develop/HEAD.)

I believe input validation should allow this, because Foreman supports
a global default puppetmaster.