why http code status is 0 when tcp_hit:none ?

[William Hanwoody <hanwoody@xxxxxxxxx>]

squid log:
218.108.56.170 - - [03/Dec/2008:20:01:08 +0800] 
6582 "GET /public/js/livecast/function.js HTTP/1.1" 0 
0 "http://xxx.com.cn/livecast/k/live.php?id=313"; "Mozilla/4.0 (compatible; 
MSIE 6.0; Windows NT 5.1; SV1; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30)" 
TCP_HIT:NONE

60.221.78.60 - - [03/Dec/2008:20:01:23 +0800] 
6988 "GET /public/js/livecast/function.js HTTP/1.1" 0 
0 "http://xxx.com.cn/livecast/k/live.php?id=313"; "Mozilla/4.0 (compatible; 
MSIE 6.0; Windows NT 5.1; SV1)" TCP_HIT:NONE