How to use Immutable.js with redux?

Taking your good example with Immutable

import {
    ACTIVATE_LOCATION
} from './actions';

import { Map } from 'immutable';

const initialState = Map({})

export let ui = (state = initialState, action) => {
  switch (action.type) {
    case ACTIVATE_LOCATION:
      return state.set('activeLocationId', action.id);
    default:
      return state;
  }
};