ENG-4645: memcheck/debug builds, which enable C++ assertions, trip
over this assertion that there is at least one element for which stats
are being gathered, which is now being actively tested in a case
where that is false.  For the record, I believe that a schema that was
just a replicated table with no indexes would have failed in the same
way for many many moons, but of course we don't have a test with that
case.