Using 'roundup-admin' and tryping to set the password 
property of a user to None doesn't work as describe. 
The following error is produced.

roundup> set user3 password=
Traceback (most recent call last):
  
File "/usr/lib/python2.4/site-packages/roundup/admin.py", 
line 1359, in run_command
    ret = function(args[1:])
  
File "/usr/lib/python2.4/site-packages/roundup/admin.py", 
line 635, in do_set
    key, value)
  
File "/usr/lib/python2.4/site-packages/roundup/hyperdb.py", 
line 849, in rawToHyperdb
    , itemid = itemid
  
File "/usr/lib/python2.4/site-packages/roundup/hyperdb.py", 
line 51, in from_raw
    m = password.Password.pwre.match(value)
TypeError: expected string or buffer