panic: assignment to entry in nil map

[solo-xwz]

how to avoid this?

[8763232]

`

func (h Header) write(w io.Writer, trace *httptrace.ClientTrace) error {
return h.writeSubset(w, nil, trace) exclude is nil？
}

func (h Header) writeSubset(w io.Writer, exclude map[string]bool, trace *httptrace.ClientTrace) error {
.......
mutex.Lock()
exclude[HeaderOrderKey] = true problem is there!
exclude[PHeaderOrderKey] = true
exclude[UnChangedHeaderKey] = true
mutex.Unlock()
......

@wangluozhe you need fix,pls!