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

module ActiveModel
  class Serializer
    class Adapter
      class NullAdapter
        def initialize(adapter)
          @attributes = adapter.attributes 
        end

        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