Description of problem:
After unregister system from webUI, virt-who will fail to communicate with subscription-manager as get return info "undefined method `inject' for nil:NilClass" from candlepin.

Version-Release number of selected component (if applicable):
candlepin-0.9.49.11-1.el7.noarch
katello-2.2.0.18-1.el7sat.noarch
Satellite-6.1.0-RHEL-6-20160321.0

How reproducible:
Always

Steps to Reproduce:
1 Register system to satellite6.1.
2 Configure virt-who monitor hyperv.
[root@sgi-xe500-01 run]# cat /etc/sysconfig/virt-who  | grep -v ^# | grep -v ^$
VIRTWHO_DEBUG=1
VIRTWHO_INTERVAL=2
VIRTWHO_HYPERV=1
VIRTWHO_HYPERV_OWNER=ACME_Corporation
VIRTWHO_HYPERV_ENV=Library
VIRTWHO_HYPERV_SERVER=10.73.5.212
VIRTWHO_HYPERV_USERNAME=administrator
VIRTWHO_HYPERV_PASSWORD=Welcome1
3 Restart virt-who 
[root@sgi-xe500-01 run]# service virt-who restart
4 Delete the system using the stage candlepin site
5.In hyperv, start/stop/pause guests.
6 Check the virt-who log in rhsm.log
[root@sgi-xe500-01 run]# tail -f /var/log/rhsm/rhsm.log
2016-03-30 02:50:26,642 [virtwho.main DEBUG] MainProcess(12420):MainThread @subscriptionmanager.py:hypervisorCheckIn:186 - Host-to-guest mapping: {
    "564D80F1-61F0-8510-87BF-57F9EC6122D7": [
        {
            "guestId": "C877953C-A19E-5149-B614-D97873C4CBD2", 
            "state": 1, 
            "attributes": {
                "active": 1, 
                "hypervisorVersion": "6.3.9600.16404", 
                "virtWhoType": "hyperv", 
                "hypervisorType": "hyperv"
            }
        }, 
        {
            "guestId": "8329390B-8359-F646-9176-27D738580E81", 
            "state": 5, 
            "attributes": {
                "active": 0, 
                "hypervisorVersion": "6.3.9600.16404", 
                "virtWhoType": "hyperv", 
                "hypervisorType": "hyperv"
            }
        }
    ]
}
2016-03-30 02:50:26,763 [virtwho.main ERROR] MainProcess(12420):MainThread @virtwho.py:send:203 - Unable to send data: Communication with subscription manager failed with code 500: undefined method `inject' for nil:NilClass

Actual results:
Virt-who get return info from candlepin as the following:
"Unable to send data: Communication with subscription manager failed with code 500: undefined method `inject' for nil:NilClass"

Expected results:
Candlepin shouldn't return "undefined method `inject' for nil:NilClass", it should return " "Communication with subscription manager failed: consumer no longer exists""

Additional info: