active_model_serializers/lib/active_model/serializer/adapter/simple_adapter.rb

module ActiveModel
  class Serializer
    class Adapter
      class SimpleAdapter < Adapter
        def to_json(options={})
          @attributes.each_with_object({}) do |(attr, value), h|
            h[attr] = value
          end.to_json # FIXME: why does passing options here cause {}?
        end
      end
    end
  end
end