为什么会出现。是否仅返回最后一项?

//-------------this is my reducer------------------------
const INITIAL_STATE = {};
export const PostReducer = (state = INITIAL_STATE, action) => {
  switch (action.type) {
    case FETCH_POSTS: {
      return _.mapKeys(action.payload.data);
    }
    default:
      return state;
  }
};

//----------this is my renderPost method ------------------------------

renderPosts = () => {
    return _.map(this.props.posts, post => {
      return (
        <li className="list-group-item" key={post.id}>
          <h3>{post.title}</h3>
        </li>
      );
    });
  };
  
 //---------mapStateToProps------------------------------
 const mapStateToProps = state => {
  return {posts: state.posts};
};
export default connect(mapStateToProps, {fetchPosts})(PostsIndex);

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