After thinking about this over the break, I decided to think that it
makes more sense for this method to be able to return null, to indicate
the absence of a response.
Previously it was required to return an "empty" message for such case,
but I think it may confuse some pipes, as such an empty message isn't
really distinguishable from a real reply that happens to be empty, which
is also valid.
I thought about having a special Message instance for such an empty
message, but I think it's just more natural to use null, especially
given that some aspects of a Message is mutable.
--
Kohsuke Kawaguchi
Sun Microsystems kohsuke.kawaguchi_at_sun.com