Description of problem:
When I use spacewalk-report with different options:
no options
--multival-separator
--multival-on-rows
I will get None (,None,) for first two when field is empty
I will get empty string (,,) for last
It doesn't matter what report - tested on users, users-system, inventory - those contain empty fields

Version-Release number of selected component (if applicable):
Satellite 5.4, spacewalk-reports-1.2.2-1.el5sat

How reproducible:
deterministic

Steps to Reproduce:
1. Connect to Satellite, install spacewalk-reports
2. try: spacewalk-report --multival-separator=. users-systems
3. try: spacewalk-report users-systems
4. try: spacewalk-report --multival-on-rows users-systems
  
Actual results:
# spacewalk-report --multival-on-rows users-systems
organization_id,user_id,username,server_id,group,admin_access
1,1,admin,1000010000,,1
1,1,admin,1000010020,,1
...

# spacewalk-report users-systems
organization_id,user_id,username,server_id,group,admin_access
1,1,admin,1000010000,None,1
1,1,admin,1000010020,None,1
...

# spacewalk-report --multival-separator=. users-systems
organization_id,user_id,username,server_id,group,admin_access
1,1,admin,1000010000,None,1
1,1,admin,1000010020,None,1
...

Expected results:
Consistent None or empty string in all versions.

Additional info:
Not really functionality problem - therefor low/low, but since one of the possible usage of reports is to parse them - it might be appreciated by customers not to add more regulars like "\(None\)\?" into parsers.