redux_post_g_secondFix.js

const combineLazyReducers = (reducers, initialState) => {
    let reducerKeys = new Set(Object.keys(reducers));
    Object.keys(initialState)
          .filter(k => !reducerKeys.has(k))
          .forEach(k => {
              reducers[k] = state => state === undefined ? null : state
          });

    return combineReducers(reducers);
}