can't parse the struct field with the lowercase about go HOT 1 CLOSED

func Test_mixed(t *testing.T) {
	should := require.New(t)
	type  AA struct {
		ID      int `json:"id"`
		Payload map[string]interface{} `json:"payload"`
		buf     *bytes.Buffer `json:"-"`
	}
	aa := AA{}
	err := UnmarshalFromString(` {"id":1, "payload":{"account":"123","password":"456"}}`, &aa)
	should.Nil(err)
	should.Equal(1, aa.ID)
	should.Equal("123", aa.Payload["account"])
}