ReactiveCocoa-MappingErrors.m

- (instancetype)fetchPerson:(NSInteger)personId {
  [[self fetchAtEndPoint: [NSString stringWithFormat: @"/person/%d", personId], mapTo: [Person class]] flattenMap: ^(id person) {
    if(!person) {
      return [RACSignal error: nil];
    } else {
      return [RACSignal return: person];
    }
  }];
}

- (instancetype)fetchAtEndPoint: (NSString *)relativePath mapTo: (Class)theClass {
 // Implementation details...
}