When you unmarhsal json to a map, always pass the reference to map object. This is very subtle and I fixed two bugs last week related to same thing.

var m map[string]string
err := json.Unmarshal(data, m)
if err != nil {
	return err
}

The code snippet above will not fail/err. But when you look at m, you will get nothing. To fix this, we need to pass the reference to m in json.Unmarshal.

var m map[string]string
err := json.Unmarshal(data, &m)
if err != nil {
	return err
}