向浏览器发送“ null”而不是“ {}”

Question

I want to able to send null to the browser as JSON, if I do this:

json.NewEncoder(w).Encode(nil)

then null will be received by the browser. However in this context:

var nearby map[string]Nearby

// ...

func GetOne(w http.ResponseWriter, r *http.Request) {
    params := mux.Vars(r)
    item := nearby[params["id"]] // item could be nil?
    json.NewEncoder(w).Encode(item)
}

if nothing exists in the map, then {} will be received by the browser instead of null...is there some way I can send null if the key is not in the map?

Answer 1

As indicated in the comments on the quesiton, the map value is a struct. A struct cannot have the value nil.

If the intent is to write null when there's no value in the map, then explicitly write the null in that case:

item, ok := nearby[params["id"]]
if ok {
   json.NewEncoder(w).Encode(item)
} else {
   io.WriteString(w, "null")
   // Can also use json.NewEncoder(w).Encode(nil), but that involves more machinery.
}