Make zero results work properly

services/httpd/handler.go

@@ -1012,12 +1012,6 @@ func (h *Handler) servePromRead(w http.ResponseWriter, r *http.Request, user met
 		h.httpError(w, err.Error(), http.StatusBadRequest)
 		return
 	}
-
-	if rs == nil {
-		err = errors.New("no store to read")
-		h.httpError(w, err.Error(), http.StatusBadRequest)
-		return
-	}
 	defer rs.Close()
 
 	resp := &remote.ReadResponse{

services/httpd/handler_test.go

@@ -581,7 +581,7 @@ func TestHandler_PromWrite(t *testing.T) {
 		if err != nil {
 			t.Fatal(err.Error())
 		}
-		expFields := models.Fields{"f64": 1.2}
+		expFields := models.Fields{"value": 1.2}
 		if !reflect.DeepEqual(fields, expFields) {
 			t.Fatalf("fields don't match\n\texp: %v\n\tgot: %v", expFields, fields)
 		}

services/storage/resultset.go

@@ -22,12 +22,21 @@ type ResultSet struct {
 	mb  *multiShardBatchCursors
 }
 
+// Close closes the result set. Close is idempotent.
 func (r *ResultSet) Close() {
+	if r == nil {
+		return // Nothing to do.
+	}
 	r.row.query = nil
 	r.cur.Close()
 }
 
+// Next returns true if there are more results available.
 func (r *ResultSet) Next() bool {
+	if r == nil {
+		return false
+	}
+
 	row := r.cur.Next()
 	if row == nil {
 		return false

services/storage/store.go

@@ -104,14 +104,14 @@ func (s *Store) Read(ctx context.Context, req *ReadRequest) (Results, error) {
 		return nil, err
 	}
 	if len(shardIDs) == 0 {
-		return nil, nil
+		return (*ResultSet)(nil), nil
 	}
 
 	var cur seriesCursor
 	if ic, err := newIndexSeriesCursor(ctx, req.Predicate, s.TSDBStore.Shards(shardIDs)); err != nil {
 		return nil, err
 	} else if ic == nil {
-		return nil, nil
+		return (*ResultSet)(nil), nil
 	} else {
 		cur = ic
 	}