[Zope3-dev] attribute index indexing None if returned from callable

[Jürgen Kartnaller]

If a callable is used to provide the value for an attribute index in 
zope.app.catalog value None is indexed. If the value is directly 
provided by an attribute None is never indexed.

I would like to see the same behavior for both cases, that means None is 
not indexed in either ways.

If no one complains I will check in the necessary changes.

Jürgen