zsql returning no results crashes dtml-call

If I have a dtml statement like:
  <dtml-call "myzsqlmethod()">
and myzsqlmethod returns no results,
then I get this error:
  Error Type: TypeError
  Error Value: object of type 'NoneType' has no len()

This is only for zsql that returns "no results" (for example, an UPDATE statement), as opposed to a query that returns an empty list of rows.

I can trace the problem to SAWrapper.query() in SQLAlchemyDA.da, specifically, the lines:
        if desc is None:
            return [], None
The DocumentTemplate code (somewhere in cDocumentTemplate) wants to compute the len() of the second item in that returned tuple, which raises the error.

I couldn't find an official API for database adapters, but http://www.zope.org/Members/petrilli/WritingADA suggests that the second item in the returned tuple should be a list. If I change the code to:
            return [], []
then it works. But I don't know if anything else relies on None in that spot to signify a query with no results.

I'm open to any sort of fix or workaround. Thanks!

SQLAlchemyDA 0.5.0 (but 0.5.1 has the same issue)
sqlalchemy-0.6.4-py2.6.egg
DocumentTemplate-2.13.1
zope2-2.13.0a4