Description of problem:
Cancelling a scheduled task via command line gives an error.  This MAY be related to https://www.redhat.com/archives/spacewalk-list/2014-February/msg00089.html
 or Bug 1402522 

Version-Release number of selected component (if applicable):

satellite-branding-5.8.0.8-1.el6sat.noarch
satellite-doc-indexes-5.8.0-1.el6sat.noarch
satellite-repo-5.8.0.2-2.el6sat.noarch
satellite-schema-5.8.0.38-1.el6sat.noarch
:
spacewalk-base-2.5.2-13.el6sat.noarch
spacewalk-base-minimal-2.5.2-13.el6sat.noarch
spacewalk-base-minimal-config-2.5.2-13.el6sat.noarch
:
postgresql-8.4.20-8.el6_9.x86_64
postgresql-jdbc-8.4.704-2.el6.noarch
postgresql-libs-8.4.20-8.el6_9.x86_64
rh-postgresql95-postgresql-9.5.7-2.el6.x86_64
rh-postgresql95-postgresql-contrib-9.5.7-2.el6.x86_64
rh-postgresql95-postgresql-libs-9.5.7-2.el6.x86_64
rh-postgresql95-postgresql-pltcl-9.5.7-2.el6.x86_64
rh-postgresql95-postgresql-server-9.5.7-2.el6.x86_64
rh-postgresql95-runtime-2.2-3.el6.x86_64
spacewalk-backend-sql-postgresql-2.5.3-157.el6sat.noarch
spacewalk-java-postgresql-2.5.14-107.el6sat.noarch
spacewalk-postgresql-2.5.0-13.el6sat.noarch
spacewalk-postgresql-server-9.5-1.el6sat.noarch
spacewalk-setup-postgresql-2.5.0-27.el6sat.noarch
:

How reproducible:
easily

Steps to Reproduce:
1. (used WebUI) schedule an update and reboot task (on one machine, here)
2. spacecmd -q -- schedule_listpending
3. spacecmd -q -- schedule_cancel 2429

Actual results:

# spacecmd -q -- schedule_listpending | awk '/201.....T07.30.00/{print $1}'
2429
2428

# spacecmd -q -- schedule_cancel 2429
ERROR: redstone.xmlrpc.XmlRpcFault: unhandled internal exception: null


# spacecmd -q -- schedule_listpending | awk '/201.....T07.30.00/{print $1}'
2429
2428


Expected results:
A message that the task is cancelled.

Additional info: