drop the *s guard

db.go

@@ -575,15 +575,7 @@ type Stats struct {
 // This is useful when obtaining stats at two different points and time and
 // you need the performance counters that occurred within that time span.
 func (s *Stats) Sub(other *Stats) Stats {
-	var diff Stats
-	if s == nil {
-		if other == nil {
-			return diff
-		} else {
-			return *other
-		}
-	}
-	diff = *s
+	var diff = *s
 	if other == nil {
 		return diff
 	}