Skip nil and zero length hits (#601)

Signed-off-by: 马庆升 <mqs@meitu.com>

plugin/storage/es/spanstore/reader.go

@@ -72,8 +72,6 @@ var (
 	// ErrUnableToFindTraceIDAggregation occurs when an aggregation query for TraceIDs fail.
 	ErrUnableToFindTraceIDAggregation = errors.New("Could not find aggregation of traceIDs")
 
-	errNilHits = errors.New("No hits in read results found")
-
 	errNoTraces = errors.New("No trace with that ID found")
 
 	defaultMaxDuration = model.DurationAsMicroseconds(time.Hour * 24)
@@ -232,8 +230,8 @@ func (s *SpanReader) multiRead(traceIDs []string, startTime, endTime time.Time)
 
 	var traces []*model.Trace
 	for _, result := range results.Responses {
-		if result.Hits == nil {
-			return nil, errNilHits
+		if result.Hits == nil || len(result.Hits.Hits) == 0 {
+			continue
 		}
 		spans, err := s.collectSpans(result.Hits.Hits)
 		if err != nil {

plugin/storage/es/spanstore/reader_test.go

@@ -144,7 +144,7 @@ func TestSpanReader_GetTraceQueryError(t *testing.T) {
 	})
 }
 
-func TestSpanReader_GetTraceNilHitsError(t *testing.T) {
+func TestSpanReader_GetTraceNilHits(t *testing.T) {
 	withSpanReader(func(r *spanReaderTest) {
 		var hits []*elastic.SearchHit
 		searchHits := &elastic.SearchHits{Hits: hits}
@@ -158,7 +158,7 @@ func TestSpanReader_GetTraceNilHitsError(t *testing.T) {
 			}, nil)
 
 		trace, err := r.reader.GetTrace(model.TraceID{Low: 1})
-		require.EqualError(t, err, "No hits in read results found")
+		require.EqualError(t, err, "No trace with that ID found")
 		require.Nil(t, trace)
 	})
 }