If we ensure that $root is never empty we can simplify this check quite a bit: `"--root '#{$root}' " if $root`.

I see at least one other place in the code where we need to check for `nil?` and `emtpy?`. I'd rather have one check for an empty string when setting the variable and then just rely on the fact that once the variable is set, it contains something more meaningful than just blanks. Of course, the user might just set it to a nonsensory value, but that's not our problem (for now).