Redux和不可变

我试图在化简函数中添加不可变。但是，Uncaught TypeError: currentState.merge is not a function当来自firebase的数据命中时，我收到错误消息。

减速器代码如下（注释代码不可变）

import C from '../../constants';
import initialState from '../initialState';
import {Map, List, fromJS} from 'immutable';

const membersInitialState = fromJS(initialState.members);

export default (currentState = membersInitialState, action) => {
  let newstate;
  switch (action.type) {
    case C.RECEIVE_MEMBER_DATA:
    /*return Object.assign({}, currentState, {
      hasReceivedData: true,
      data: action.data
    });*/
    return currentState.merge({
      hasReceivedData: true,
      data: action.data
    });
    //default: return currentState || initialState.members;
  }
  return currentState;
}

rootReducer如下

import membersReducer from './members';

function rootReducer (state, action){
    return {
        members: membersReducer(state.members, action)
    }
};

export default rootReducer;