Get "null" from json.NewEncoder(bodyBuf).Encode(body) of nil

[mason-liu]

For below code fragment

bodyBuf := &bytes.Buffer{}
var body interface{}
json.NewEncoder(bodyBuf).Encode(body)
fmt.Printf("%v", bodyBuf)

the output is “null” which is weird, since it is json encode, I prefer empty string or error

[lizhiyuzhong (Retr0)]

Here the reason which i get it by debug. The var, body, which type is interface, is not string type. So when u use it without initing it, it is null.
U can turn body to string type or add a " if " sentence if u prefer empty string or error.

[mason-liu]

thanks @lizhiyuzhong, but my understanding is, it should not return a string “null” since it is in json package, I think adding logic here https://github.com/golang/go/blob/master/src/encoding/json/stream.go#L202 makes more sense.
“”, “{}” or error is better than “null”

[skillian (Sean Killian)]

The encoding/json documentation says this:

Interface values encode as the value contained in the interface. A nil interface value encodes as the null JSON value.

The value of body is nil and so it seems reasonable to encode it as a JSON null.

[lizhiyuzhong (Retr0)]

Yes, i agree your understanding. When Encoding the “body”, the logic in line 219 will write “null” in a []byte. Changing here makes more sense as u say.

[mason-liu]

Thanks Sean, I did not notice the doc you mentioned, and seems it is the standard in Go that all nil value including slice will be marshaled to null, really good to know