running /sbin/restart with no arguments restarts services

Accidentally ran `/sbin/restart` (symlink to `/sbin/initctl`) without arguments as my regular user, and unity was restarted (possibly amongst other things). I would expect it to exit immediately with an error code, given its usage and manpage (initctl (8)).

Easy to reproduce.

~$ dpkg -S `which restart`
upstart: /sbin/restart

~$ restart --help
Usage: restart [OPTION]... JOB [KEY=VALUE]...
Restart job.
...

~$ restart
unity7 start/killed, process 12622

== Environment ==

~$ lsb_release -rd
Description: Ubuntu 16.04 LTS
Release: 16.04

~$ apt-cache policy upstart
upstart:
  Installed: 1.13.2-0ubuntu21
  Candidate: 1.13.2-0ubuntu21.1
  Version table:
     1.13.2-0ubuntu21.1 500
        500 http://ca.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages
 *** 1.13.2-0ubuntu21 500
        500 http://ca.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status