Red Hat Satellite v 5.8 throws traceback with error: "TypeError, cannot marshal None unless allow_none is enabled" on RHEL clients upgraded from RHEL 6 -> RHEL 7

Issue

• Satellite receives following trackback message after client base OS upgraded from RHEL 6 to RHEL 7.

Exception Handler Information
Traceback (most recent call last):
 File "/usr/lib/python2.6/site-packages/spacewalk/server/apacheRequest.py", line 135, in call_function
   response = func(*params)
 File "/usr/share/rhn/server/handlers/xmlrpc/registration.py", line 849, in upgrade_version
   return server.system_id()
 File "/usr/lib/python2.6/site-packages/spacewalk/server/rhnServer/server_class.py", line 143, in system_id
   return self.cert.certificate()
 File "/usr/lib/python2.6/site-packages/spacewalk/server/rhnServer/server_certificate.py", line 131, in certificate
   x = xmlrpclib.dumps((dump,))
 File "/usr/lib64/python2.6/xmlrpclib.py", line 1132, in dumps
   data = m.dumps(params)
 File "/usr/lib64/python2.6/xmlrpclib.py", line 677, in dumps
   dump(v, write)
 File "/usr/lib64/python2.6/xmlrpclib.py", line 699, in __dump
   f(self, value, write)
 File "/usr/lib64/python2.6/xmlrpclib.py", line 780, in dump_struct
   dump(v, write)
 File "/usr/lib64/python2.6/xmlrpclib.py", line 699, in __dump
   f(self, value, write)
 File "/usr/lib64/python2.6/xmlrpclib.py", line 703, in dump_nil
   raise TypeError, "cannot marshal None unless allow_none is enabled"
TypeError: ('cannot marshal None unless allow_none is enabled', {'username': None, 'operating_system': 'redhat-release-server', 'description': 'Initial Registration Parameters:\nOS: redhat-release-server\nRelease: 6Server\nCPU Arch: x86_64', 'checksum': 'f2126f66ee6e168b46cab4f08318bedb0d75258f649843726f2aa71c71086781', 'profile_name': 'client.example.com', 'system_id': 'ID-10000xxxxx', 'architecture': 'x86_64-redhat-linux', 'os_release': '7Server', 'fields': ['system_id', 'os_release', 'operating_system', 'architecture', 'type'], 'type': 'REAL'})