Reactjs reduxthunk 调度方法触发未定义的操作

这是我在玩的代码

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，我先发送REQ_USER_INIT，然后发送REQ_USER_DATA.我应该记录两个动作，但我得到3个.第二个动作是undefined，我正在努力找出它的原因.是redux-thunk的错误还是我做错了什么？

以下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}