message: initialize the default value
diff: @@ -3,9 +3,9 @@ import uuidv4 from "uuid/v4";
  export default class Command {
  id = null;
  - @observable command = null;
  - @observable target = null;
  - @observable value = null;
  + @observable command = "";
  + @observable target = "";
  + @observable value = "";
  constructor(id = uuidv4()) {
  this.id = id;
  