了解RACSignal错误

我目前正在ReactiveCocoa中迈出第一步,并且我经历了一些陡峭的学习曲线来理解这些原理.

无论如何这里是我已经提出的.

我将NSArray属性绑定到RACSignal,以便能够通过网络对传入的JSON数据做出反应.

- (void)updateRandomUserData 
{
    @weakify(self);
    RAC(self, users) = [[self fetchRandomUserData] doNext:^(NSDictionary *json){
    @strongify(self);
    NSMutableArray *randomUsers = [NSMutableArray array];
        for (NSDictionary *dict in json[@"data"]) {
           BKRandomUser *randomUser = [MTLJSONAdapter modelOfClass:[BKRandomUser class] fromJSONDictionary:dict error:nil];
           [randomUsers addObject:randomUser];
        }

        self.users = randomUsers;
    }];
}

信号创建如下所示:

- (RACSignal *)fetchRandomUserData
{

    return [[RACSignal createSignal:^RACDisposable *(id subscriber) {

      NSURLRequest *request = [NSURLRequest requestWithURL:url];

      AFJSONRequestOperation *operation = [AFJSONRequestOperation JSONRequestOperationWithRequest:request success:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON) {
      [subscriber sendNext:JSON];
      } failure:^(NSURLRequest *request, NSHTTPURLResponse *response, id JSON, NSError *error) {
        [subscriber sendError:error];
      }];

      [operation start];

      return [RACDisposable disposableWithBlock:^{
          [operation cancel];
      }];

      }] doError:^(NSError *error) {
        NSLog(@"error: %@", [error description]);
    }];

}

现在,当Web服务不提供任何我希望对此做出反应的数据时.现在应用程序崩溃了以下声明,我真的不明白:

*由于未捕获的异常'NSInternalInconsistencyException'而终止应用程序,原因:'从名称收到错误:[[+ createSignal:] -doError:] -doNext:在关键路径"users"的绑定中:( null)'

我在这里错过了什么？

谢谢!