Reactjs ReactRedux 没有为关键 coins提供减速器

我不知道为什么会出现以下错误.

我只是在建立我的store ，行动和减速器，我还没有打电话给调度.

预期

应用程序运行正常，Redux状态未更新

后果

import React from 'react'
import ReactDOM from 'react-dom'

import { createStore, applyMiddleware, compose } from 'redux'
import { Provider } from 'react-redux'
import thunk from 'redux-thunk'
import reducer from './reducer'

import App from './App'
import css from './coinhover.scss'

const element = document.getElementById('coinhover');

const store = createStore(reducer, compose(
    applyMiddleware(thunk),
    window.__REDUX_DEVTOOLS_EXTENSION__ && window.__REDUX_DEVTOOLS_EXTENSION__()
));

ReactDOM.render(
    <Provider store={ store }>
        <App />
    </Provider>, element);

import { combineReducers } from 'redux'
import { coins } from './coins'

export default combineReducers({
    coins
});

import * as api from '../../services/api'
import { storage, addToPortfolio } from '../../services/coinFactory'

export const ADD_COIN = 'ADD_COIN'

export function getCoin(coin) {
    return dispatch => {
        api.getCoin(coin)
            .then((res_coin)  => addToPortfolio(res_coin))
            .then((portfolio) => dispatch(updatePortfolio(portfolio)));
    }
}

export function updatePortfolio(portfolio) {
    return {
        type: ADD_COIN,
        portfolio
    }
}

import { ADD_COIN } from './actions'

const initialState = [];

export default (state = initialState, action) => {
    switch(action.type) {
        case ADD_COIN:
            return action.portfolio;
        default:
            return state;
    }
}