if you try to delete a dbm mapping entry by passing in a key that is
None, you raise a TypeError.

This seems to be harmless, but currently this exception is not trapped
in session.py.  i ran into this when i had configured my browser to
reject cookies and then clicked the logout link on the session demo.

note that with your browser rejecting cookies, if you sit on the demo
login screen and click refresh, the session list grows and grows.

Regards,

--
Mark Bucciarelli, www.hubcapconsulting.com
    He who receives an idea from me, receives instruction himself
without lessening mine; as he who lights his taper at mine receives
light without darkening me.   -- Thomas Jefferson