config-get on an int set to 0 does not return '0' but an empty string

root@ip-10-98-47-86:/var/lib/juju/units/mc7-0/charm# config-get|grep udp
{u'request-limit': -1, u'slab-page-size': -1, u'min-item-size': -1, u'disable-large-pages': u'no', u'disable-cas': u'no', u'connection-limit': 1024, u'udp-port': 0, u'threads': -1, u'disable-auto-cleanup': u'no', u'factor': u'-1.0', u'tcp-port': 11211, u'extra-options': u'', u'size': u'2048'}
root@ip-10-98-47-86:/var/lib/juju/units/mc7-0/charm# config-get udp-port
root@ip-10-98-47-86:/var/lib/juju/units/mc7-0/charm#

I would have expected 'config-get udp-port' to print 0, not an empty string.

juju:
  Installed: 0.5+bzr427-1juju2~oneiric1
  Candidate: 0.5+bzr427-1juju2~oneiric1
  Version table:
 *** 0.5+bzr427-1juju2~oneiric1 0
        500 http://ppa.launchpad.net/juju/pkgs/ubuntu/ oneiric/main i386 Packages
        100 /var/lib/dpkg/status
     0.5+bzr398-0ubuntu1 0
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu/ oneiric/universe i386 Packages