remove the if statement to actually yield empty series

src/engine/engine.go

@@ -192,13 +192,11 @@ func (self *QueryEngine) Close() {
 			Name:   series.Name,
 			Fields: series.Fields,
 		}
-		if len(s.Points) > 0 {
 		err = self.yield(s)
 		if err != nil {
 			break
 		}
 	}
-	}
 
 	if self.isAggregateQuery {
 		self.runAggregates()