Looks like a bug to me - I believe that the gateway should, as you say, return an empty list if there are no results. A gateway should never behave this way.
It gets a bit more tricky if 'expectSingleResult' is true (we can't return a null payload), so I suspect we'd have to return an empty list there too - but that's a bit messy because the result type will depend on the data. Maybe we'd have to throw an exception in that case.
Please go ahead and create a JIRA ticket and we can start a dialog of how to fix the problem there.
Gary P. Russell
Spring Integration Team
SpringSource, a division of VMware