CompletionSuggester can return partial information (no _id and _score)

We are seeing this behavior from times to times, we see a spike on invalid responses returned by the completion suggester: the options returned may be "partial". By partial response I mean that the individual hits are not provided with the usual information retrieved during the fetch_phase.

In this case only text seems to be available, _id and _score are not populated.

I'm almost sure that this happens only when a node was dropped from the cluster or during a rolling restart.

Looking at the code this behavior seems to line-up with a TODO comment in SearchPhaseController.java where a failure during the fetch phase may produce this inconsistency.