There is so many unnecessary nullability taken,so can we remove unnecessary nullability taken?

Hello! 最近在看您写的MVCS框架 ，KVO模块有个地方不太理解：
[info.observedObject removeObserver:info.observingObject forKeyPath:info.keyPath]; 既然已经移除了kvo 。那下面这段代码看着不是很懂：

        NSObject *otherObject = nil;
        if (info.observedObject != registeredObject) {
            otherObject = info.observedObject;
        } else if (info.observingObject != registeredObject) {
            otherObject = info.observingObject;
        }
        
        NSMutableArray *infosForOtherObject = [otherObject mi_associatedObjectForKey:kMIKVOInfoKey];
        [infosForOtherObject removeObject:info];

看了你画的mvcs图，非常棒！现在我有一个疑问，网络请求在MVVM中的标准位置是哪里？是直接放到view model中还是单写一个service类中？

`[[MIMediator sharedMediator] viewControllerWithScene:scene context:self.pipeline.contextForSearch];
[self.navigationController pushViewController:viewController animated:YES];

`
只是参数的向前传递 有没有back之后的向后传递方式，或者用一种全局性的参数传递方式呢，比如说通知。

pragma mark - KVO

• (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary<NSKeyValueChangeKey,id> *)change context:(void *)context {

  __MIKVOInfo *info = (__bridge __MIKVOInfo *)(context);
  if (info.changed) {
  id newValue = [change valueForKey:NSKeyValueChangeNewKey];
  info.changed([newValue isKindOfClass:[NSNull class]] ? nil : newValue);
  }
  }

报错no type protocol name 'NSKeyValueChangeKey'
是我步骤有问题么
xcode 7.3.1