added root in grape api but not included in response

I am following this article to learn about writing api using grape gem. But in the response I am not getting the root key. Here is my directory structure,

app
 |––controllers
       |––api
           |––base.rb
           |––v1
               |––base.rb
               |––graduates.rb

In app/controllers/api/v1/graduates.rb:

module API
  module V1
    class Graduates < Grape::API
      include API::V1::Defaults
  resource :graduates do
    desc "Return all graduates"
    get "", root: :graduates do
      Graduate.all
    end

    desc "Return a graduate"
    params do
      requires :id, type: String, desc: "ID of the 
        graduate"
    end
    get ":id", root: "graduate" do
      Graduate.where(id: permitted_params[:id]).first!
    end
  end
end

end end

in app/controllers/api/v1/defaults.rb

module API
  module V1
    module Defaults
      extend ActiveSupport::Concern
  included do
    prefix "api"
    version "v1", using: :path
    default_format :json
    format :json
    formatter :json, 
         Grape::Formatter::ActiveModelSerializers

    helpers do
      def permitted_params
        @permitted_params ||= declared(params, 
           include_missing: false)
      end

      def logger
        Rails.logger
      end
    end

    rescue_from ActiveRecord::RecordNotFound do |e|
      error_response(message: e.message, status: 404)
    end

    rescue_from ActiveRecord::RecordInvalid do |e|
      error_response(message: e.message, status: 422)
    end
  end
end

end end

I have used grape-active_model_serializers gem to serialize like the following, In app/serializers/graduate_serializer.rb

class GraduateSerializer < ActiveModel::Serializer
  attributes :id, :name
end

I got the following output. [{"id":1,"name":"aaaa"},{"id":2,"name":"bbbb"},{"id":3,"name":"cccc"},{"id":4,"name":"dddd"}]

But As I added get "", root: :graduates do in app/controllers/api/v1/graduates.rb file, I am expecting the following output,

{"graduates": [{"id":1,"name":"aaaa"},{"id":2,"name":"bbbb"},{"id":3,"name":"cccc"},{"id":4,"name":"dddd"}]}

What I am missing. why graduates is not added as root. Help me to fix this issue.

Dirty fix: use in app/controllers/api/v1/graduates.rb

get "" do
    { graduates: Graduate.all }
end

Or you can delete gem grape-active_model_serializers, delete class GraduateSerializer, delete row formatter :json, Grape::Formatter::ActiveModelSerializers from defaults.rb, and add gem grape-entity to Gemfile, install it, add code to app/app/entities/graduate_entity.rb:

class GraduateEntity < Grape::Entity
  root 'graduates', 'graduate'

  expose :id
  expose :name
end

Change code in app/app/controllers/api/v1/graduates.rb:

get "" do
  present Graduate.all, with: GraduateEntity
end