Expected the root reducer to be a function. Instead, received: ''

Question

I receive an error when following a YouTube crash course on redux:

redux.js:158 Uncaught Error: Expected the root reducer to be a function. Instead, received: ''

at createStore (redux.js:158:1) | at redux.js:682:1 | at createStore (redux.js:154:1) | at ./src/state/store.js (store.js:5:1)

I suspect the error is inside store.js, but I'm not able to debug it. And, why '' is returned? Very much grateful for your help.

store.js

import { legacy_createStore as createStore, applyMiddleware } from "redux";
import reducers from "./reducers/index"
import thunk from "redux-thunk"

export const store = createStore(
    reducers,
    {},
    applyMiddleware(thunk)
) 

reducers/index.js

import { combineReducers } from "redux";
import accountReducer from "./accountReducer";

const reducers = combineReducers ({
    account : accountReducer
});

export default reducers;

reducers/accountReducer.js

const reducer = (state = 0, action) => {
    switch (action.type) {
        case "deposit":
            return state + action.payload;
        case "withdraw":
            return state - action.payload;
        default:
            return state
    }
};

export default reducer;

App.js

import {useSelector, useDispatch} from "react-redux"
import {bindActionCreators} from "redux"
import {actionCreators} from "./state/index"

function App() {

  const account = useSelector((state) => state.acoount );
  const dispatch = useDispatch()

  const {depositMoney, withdrawMoney} = bindActionCreators(actionCreators, dispatch)
  

  return (
    <div className="App">
      <h1>{account}</h1>
      <button onClick={() => depositMoney(1000)}>Deposit</button>
      <button onClick={() => withdrawMoney(1000)}>Withdraw</button>
    </div>
  );
}

export default App;

index.js

import React from 'react';
import ReactDOM from 'react-dom/client';
import './index.css';
import App from './App' ;
import reportWebVitals from './reportWebVitals';
import { Provider } from 'react-redux';
import {store} from './state/store'
const root = ReactDOM.createRoot(document.getElementById('root'));

root.render(
  <React.StrictMode>
    <Provider store = {store}>
    <App />
    </Provider>
  </React.StrictMode>
);

reportWebVitals();