ios - AFNetworking 错误信息：NSCocoaErrorDomain Code=3840

App 使用很久了，昨天出现一个bug，网络请求总失败。调试打印，发现是这样的错误：

AFHTTPRequestOperation *operation = [manager POST:URLString parameters:param success:^(AFHTTPRequestOperation *operation, id responseObject) {
    if (successBlock) {
        successBlock(responseObject);
    }
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
    if (failureBlock) {
        failureBlock(error);
    }
    NSLog(@"%@", error);
}];

Error Domain=NSCocoaErrorDomain Code=3840 "JSON text did not start with array or object and option to allow fragments not set." UserInfo={NSDebugDescription=JSON text did not start with array or object and option to allow fragments not set., NSUnderlyingError=0x15eb52e0 {Error Domain=com.alamofire.error.serialization.response Code=-1011 "Request failed: bad gateway (502)" UserInfo={com.alamofire.serialization.response.error.response= { URL: http://xxx.com } { status code: 502, headers { Connection = "keep-alive"; "Content-Length" = 173; "Content-Type" = "text/html"; Date = "Mon, 01 Feb 2016 03:35:51 GMT"; Server = "nginx/1.5.12"; } }, NSErrorFailingURLKey=http://xxx.com, NSLocalizedDescription=Request failed: bad gateway (502)

有大神遇到过吗？App 使用很久了，头一次出现这样的 bug, 因此可以排除 manager 的配置问题。