gem 'active_model_serializers', github: 'rails-api/active_model_serializers', branch: '0-10-stable'

class Item
  include Mongoid::Document
  include Mongoid::Timestamps
end

def index
  render json: Item.all
end

-----

Failure/Error: get 'index'
NoMethodError:
undefined method `new' for nil:NilClass