Nagios checks fail

Using cs:squid-reverseproxy-7, and adding a relation with nrpe, the outcome is a nagios check of:

# check squidpeers
command[check_squidpeers]=/usr/lib/nagios/plugins/check_squidpeers -p 3128 -w 50

Running this commands gives:

ubuntu@juju-f66069-charm-testing-squid-reverseproxy-trusty-20-1:~$ /usr/lib/nagios/plugins/check_squidpeers -p 3128 -w 50
Traceback (most recent call last):
  File "/usr/lib/nagios/plugins/check_squidpeers", line 87, in <module>
    sys.exit(main())
  File "/usr/lib/nagios/plugins/check_squidpeers", line 81, in main
    retcode, message = get_status(peers, args.weight)
  File "/usr/lib/nagios/plugins/check_squidpeers", line 51, in get_status
    perc = calculate_perc_up(peers)
  File "/usr/lib/nagios/plugins/check_squidpeers", line 46, in calculate_perc_up
    return ((reduce(iadd, [1. for i in peers if i['status'] == STATUS_UP]))
TypeError: reduce() of empty sequence with no initial value