redux-thunk dispatch方法触发未定义的动作

所以这是我正在玩的代码

import { createStore, applyMiddleware } from 'redux'
    import thunk from 'redux-thunk'
    import axios from 'axios'

    const initialState = {
        user: {},
        requesting: false,
        err: null
    }

    const reducer = (state = initialState, action) => {
        switch (action.type) {
            case 'REQ_USER_INIT': return { ...state, requesting: true }
            case 'REQ_USER_DATA': return { ...state, requesting: false, user: action.user }
            case 'REQ_USER_ERR': return { ...state, requesting: false, err: action.err }
        }
        return state;
    }

    const logger = (store) => (next) => (action) => {
        let previous = JSON.stringify(store.getState())
        next(action)
        console.log(
            'action: ' + JSON.stringify(action) +
            '\n\tprevious: ' + previous +
            '\n\tcurrent: ' + JSON.stringify(store.getState())
        )
    }

    const store = createStore(reducer, applyMiddleware(logger, thunk))

    store.dispatch((dispatch) => {
        dispatch({ type: 'REQ_USER_INIT' })

        // Fake Online REST API for Testing and Prototyping
        // break url to get an error response
        let usersEndpoint = 'https://jsonplaceholder.typicode.com/users/1'

        axios.get(usersEndpoint)
            .then((response) => {
                dispatch({
                    type: 'REQ_USER_DATA',
                    user:  {
                        id: response.data.id,
                        username: response.data.username,
                        email: response.data.email,
                    }
                })
            })
            .catch((error) => {
                dispatch({
                    type: 'REQ_USER_ERR',
                    err: error.message
                })
        })
    })

我相信这很简单，对吧？收到回复后，我会发送 REQ_USER_INIT 然后发送 REQ_USER_DATA . 我应该记录两个动作，但是我得到3.第二个动作是 undefined ，我很想知道是什么导致它 . 这是 redux-thunk 的错误还是我做错了什么？

这是我的控制台的输出 .

action: {"type":"REQ_USER_INIT"}
    ·previous: {"user":{},"requesting":false,"err":null}
    ·current: {"user":{},"requesting":true,"err":null}
    action: undefined
    ·previous: {"user":{},"requesting":false,"err":null}
    ·current: {"user":{},"requesting":true,"err":null}
    action: {"type":"REQ_USER_DATA","user":{"id":1,"username":"Bret","email":"Sincere@april.biz"}}
    ·previous: {"user":{},"requesting":true,"err":null}
    ·current: {"user":{"id":1,"username":"Bret","email":"Sincere@april.biz"},"requesting":false,"err":null}