Why is prevState argument null in calculateState method in Flux?

Question

I set state in constructor this.state = {};, but prevState argument in calculateState method is null. Where should I set initial state of container?

class QuestionnairesContainer extends Component {
  static getStores() {
    return [QuestionnairesStore];
  }

  static calculateState(prevState) {
    return {
      questionnairesList: QuestionnairesStore.getState().questionnairesList,
      pagingObject: prevState.pagingObject
    };
  }

  constructor(props) {
    super(props);
    this.state = {
      pagingObject: someData
    };
  }

  render() {
    return (
      <section>
      </section>
    );
  }
}

export default Container.create(QuestionnairesContainer);

Answer 1

I have found a solution on flux GitHub.

  static calculateState(prevState) {
    const init = prevState ? {} : {
      pagingObject: someData,
    };
    return {
      ...init,
      questionnairesList: QuestionnairesStore.getState().questionnairesList
    };
  }
  constructor(props) {
      super(props);
  }