Description of problem:
see steps to reproduce

Version-Release number of selected component (if applicable):
5.0.1

How reproducible:
three times in row

Steps to Reproduce:
1. 5.0.1 satellite with rhel5 and vt channel
2. rhel5 server with some xen created manualy
3. register server to satellite
4. create new rhel5 pv xen quest on that server
  
Actual results:
Traceback (most recent call last):
  File "/usr/share/rhn/server/apacheRequest.py", line 108, in call_function
    response = apply(func, params)
  File "/usr/share/rhn/server/handlers/xmlrpc/queue.py", line 272, in get
    ret = self.__getV2(action)
  File "/usr/share/rhn/server/handlers/xmlrpc/queue.py", line 86, in __getV2
    xmlblob = xmlrpclib.dumps(result, methodname=action['method'])
  File "/usr/lib/python2.3/xmlrpclib.py", line 961, in dumps
    data = m.dumps(params)
  File "/usr/lib/python2.3/xmlrpclib.py", line 604, in dumps
    dump(v, write)
  File "/usr/lib/python2.3/xmlrpclib.py", line 616, in __dump
    f(self, value, write)
  File "/usr/lib/python2.3/xmlrpclib.py", line 620, in dump_nil
    raise TypeError, "cannot marshal None unless allow_none is enabled"
TypeError: cannot marshal None unless allow_none is enabled

Expected results:
get actions and proceed.

Additional info: