Make sure to return Immutable objects in reducers

products.reducer.js

 [ensureProducts]: (products_data, token)=>{
    if (products_data === null){
      return loop(
        products_data,
        Effects.promise(()=>{
          let api = new ProductsApi(token);
          return api.index()
            .then(productsRetrieved)
        })
      )
    }
    return products_data;
  },

  // products_data from API response.
  [productsRetrieved]: (_products_data, new_products_data)=>{
    // return new_products_data <- not preferred. This is a plain JS object.
    return Immutable.fromJS(new_products_data); // <- preferred
  },