bugfix, delete the sid if it's values is empty

* regenerate sid, if the old key doesn't exists, set the new one directly

@@ -60,14 +60,15 @@ func (rs *RedisSessionStore) SessionID() string {
 }
 
 func (rs *RedisSessionStore) SessionRelease(w http.ResponseWriter) {
+	c := rs.p.Get()
+	defer c.Close()
+
 	// if rs.values is empty, return directly
 	if len(rs.values) < 1 {
+		c.Do("DEL", rs.sid)
 		return
 	}
 
-	c := rs.p.Get()
-	defer c.Close()
-
 	b, err := encodeGob(rs.values)
 	if err != nil {
 		return
@@ -155,8 +156,15 @@ func (rp *RedisProvider) SessionRegenerate(oldsid, sid string) (SessionStore, er
 	c := rp.poollist.Get()
 	defer c.Close()
 
-	c.Do("RENAME", oldsid, sid)
-	c.Do("EXPIRE", sid, rp.maxlifetime)
+	if existed, _ := redis.Int(c.Do("EXISTS", oldsid)); existed == 0 {
+		// oldsid doesn't exists, set the new sid directly
+		// ignore error here, since if it return error
+		// the existed value will be 0
+		c.Do("SET", sid, "", "EX", rp.maxlifetime)
+	} else {
+		c.Do("RENAME", oldsid, sid)
+		c.Do("EXPIRE", sid, rp.maxlifetime)
+	}
 
 	kvs, err := redis.String(c.Do("GET", sid))
 	var kv map[interface{}]interface{}