AFNetworking Http header sometime is nil

I have a very strange problem. when i use afnetworking with http header,sometimes the servers can not get my http header value,it's nil,nothing in header. i have no idea why.

this is my code:

NSString *url = [NSString stringWithFormat:@"%@%@",[YJHttpService serverDomain],method];
[manger.requestSerializer setValue:@"1" forHTTPHeaderField:@"source"];
[manger.requestSerializer setValue:user.user.token forHTTPHeaderField:@"token"];

NSString *version = [[[NSBundle mainBundle] infoDictionary] objectForKey:@"CFBundleShortVersionString"];
NSString *versionCode = [version stringByReplacingOccurrencesOfString:@"." withString:@""];
[manger.requestSerializer setValue:version forHTTPHeaderField:@"version"];
[manger.requestSerializer setValue:versionCode forHTTPHeaderField:@"versionCode"];