Possible AMS 0.10 bug

Gemfile

source "https://rubygems.org"

gem "active_model_serializers", github: "rails-api/active_model_serializers"
  

OUT

$ ruby src.rb

//////////////
{:name=>"sebastian"}
//////////////
/Users/skale/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/bundler/gems/active_model_serializers-fc6276cab836/lib/active_model/serializer.rb:193:in `dup': can't dup NilClass (TypeError)
	from /Users/skale/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/bundler/gems/active_model_serializers-fc6276cab836/lib/active_model/serializer.rb:193:in `attributes'
	from /Users/skale/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/bundler/gems/active_model_serializers-fc6276cab836/lib/active_model/serializer/adapter/json.rb:14:in `block in serializable_hash'
	from /Users/skale/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/bundler/gems/active_model_serializers-fc6276cab836/lib/active_model/serializer/adapter.rb:53:in `cache_check'
	from /Users/skale/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/bundler/gems/active_model_serializers-fc6276cab836/lib/active_model/serializer/adapter/json.rb:13:in `serializable_hash'
	from /Users/skale/.rbenv/versions/2.2.2/lib/ruby/gems/2.2.0/bundler/gems/active_model_serializers-fc6276cab836/lib/active_model/serializer/adapter.rb:23:in `as_json'
	from src.rb:19:in `render_json'
	from src.rb:42:in `<main>'

src.rb

require 'bundler/setup'
require 'active_model_serializers'
require 'json'

def model *attribute_names

  Struct.new(*attribute_names) do
    # include ActiveModel::Model
    include ActiveModel::Serialization

    def attributes
      to_h
    end
  end

end

def render_json serializer
  puts ActiveModel::Serializer::Adapter::Json.new(serializer).as_json
end

# CLASSES

User = model :name, :age

class UserSerializer < ActiveModel::Serializer
  attribute :name
end

# INSTANCES

someone = User.new "sebastian", 30

# TEST

puts "//////////////"

render_json UserSerializer.new(someone)

puts "//////////////"

render_json ActiveModel::Serializer.new(someone) # exception

puts "//////////////"