Handle is invoke method of Middleware. Result is the data to be processed. GatherCallback is a callback for processing. GatherCallback accepts Result | undefined.
handle是Middleware类被调用时使用的方法, result为待处理Result类型, 如果传入值为string类型, 会自动转为["undefined", string] GatherCallback为处理完毕时的回调
Gather (inherited from Finisher) can be used as the last middleware on the next call path, it will call GatherCallback ,but return false instead of result
Gather(继承Finisher)可以作为一个next调用路径上的最后一个middleware, 它会调用GatherCallback，但不会返回result而是返回false