无法读取未定义的属性“map”-react,redux

我试图在我的组件中显示文章列表,我的“ArticleList.js”组件中出现“cannot read property‘map’of undefined”错误。我的代码怎么了? 而且当我写文章时,它是未定义的。

我的减速器中有以下代码:

 const initialState = {
  articles: [],
  loading: false,
  error: null
  };


export default (state=initialState, action) => {
switch (action.type) {
    case GET_ARTICLES:
      return {
         ...state,
         articles: action.payload,
         loading: false
     };

行动代码:

 export const getArticles =()=> dispatch =>{
 fetch('http://localhost:8000/api/articles/')
.then(handleErrors)
.then(res => dispatch(
    {
        type : GET_ARTICLES,
        payload: res.json
    }
))}

组件代码:

 componentDidMount() {
     this.props.getArticles();
 }

render() {
    const { articles } = this.props.article;

return (
  <div>
    <div>
      <div>
        {articles.map(({ id, header }) => (
          <div key={id} timeout={500} className="fade">
            <div>
              <button className="remove-btn" onClick={this.onDeleteClick.bind(this, id)} >Remove</button>
              {header}
            </div>
          </div>
        ))}
      </div>
    </div>
  </div>
);
}
}

   const mapStateToProps = state => ({
        article: state.article
    });

   export default connect(
        mapStateToProps, { getArticles} )(ArticleList);

抱歉,大量的代码被丢弃了,这一切都是相关的,我相信错误就在有未定义的首字母的地方,但是我看不出我遗漏了定义什么。