It's fine if `additional_home_domains` doesn't exist - it's just blank and fails the test.

Let's discuss on Monday about commonizing the ways of adding a parameter to `DAEMON_ARGS`.  I think the `if ... then ... fi ` vs `[ ! ... ] || ...` distinction makes sense - the former is better for more complex expressions and the latter for simpler.  The `..._arg` approach vs directly manipulating `DAEMON_ARGS` is more interesting.