Comment # 8 on bug 956558 from Neil Brown

> Why is 
> 
>   ConditionPathExists=/etc/krb5.keytab
> 
> uses in lieu of that config option to make that decision?

Partly because that it what upstream nfs-utils does, and there is a lot of
value in using the same systemd unit files as upstream (but then, I put that
stuff upstream, that that isn't really an excuse).

Partly because systemd doesn't make it at all easy to selectively
enable/disable services using a env variables in a config file.

Is this causing any actual problems apart from the unsightly error message?  If
not it might be simplest just to find a way to hide the error message.