e_book_backend_summary_is_summary_query is failing

Hey all.  I'm writing an evolution connector for the Zimbra Collaboration Suite (www.zimbra.com).  In my addressbook code, I'm calling e_book_backend_summary_is_summary_query on a query that looks like this: 

(contains "x-evolution-any-field"  "")

e_book_backend_summary_is_summary_query is failing when passed that query everytime. I'm pretty new to all this, so excuse the naive question...why is this failing?  What should I be passing to e_book_backend_summary_is_summary_query to get it to return all of the ids that it knows about?  I snuck a peek or two at the implementation of e_book_backend_summary_is_summary_query and didn't really understand what it was trying to do.

Thanks for any help you could give me,

Scott