I am fetching data (an object) into a redux state and showing into textarea when user clicks on edit:

const regionData = useSelector((state) => state.myReducer.userDetailList.region);

but first time it gives me below error:

Uncaught TypeError: Cannot read properties of undefined (reading 'region')

also this error occurred when i changed code as per eslint suggestion:

i.e. 
Use an object spread instead of `Object.assign` eg: `{ ...foo }`

Old Code:

return Object.assign({}, state, {
    userDetailList: {
        region: action.userDetailsPayload.region,
    },
});

New Code:

 const userDetailList = {
     region: action.userDetailsPayload.region,
 };

 return { ...state, ...userDetailList };

As a result userDetailList showing as BLANK in Chrome redux-devtool. its working with old code (Object.assign)

I am new to react and redux, so any help is much appreciated. Thanks!