Comment 2 for bug 142410

I agree. So this means the behavior should be that:

* If an attribute error is raised by a callable attribute during indexing, the object will be
  discarded and the error trapped (Perhaps with a blather log entry). This should hold true for
  indexes and metadata.

* Objects that are missing an attribute should not be in indexes for that attribute. Doing so is
  a waste of resources not to mention inconsistent.

These rules should be documented in the ZCatalog and PlugInIndex interfaces.