source 'https://rubygems.org'
gem 'rails', '4.0.1'
gem 'pg'
gem "transitions", :require => ["transitions", "active_model/transitions"]

class CreateUsers < ActiveRecord::Migration
  def change
    create_table :users do |t|
      t.string :status
    end
  end
end

class User < ActiveRecord::Base
 include ActiveModel::Transitions
 state_machine :attribute_name => :status, :initial => :new do
  state :registered
 end
end

➜  app1  rails c
Loading development environment (Rails 4.0.1)
irb(main):001:0> u = User.new
NoMethodError: undefined method `call_action' for nil:NilClass
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/transitions-0.1.11/lib/active_model/transitions.rb:93:in `set_initial_state'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/activesupport-4.0.1/lib/active_support/callbacks.rb:375:in `_run__1719794837482552169__initialize__callbacks'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/activesupport-4.0.1/lib/active_support/callbacks.rb:80:in `run_callbacks'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/activerecord-4.0.1/lib/active_record/core.rb:188:in `initialize'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/activerecord-4.0.1/lib/active_record/inheritance.rb:27:in `new'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/activerecord-4.0.1/lib/active_record/inheritance.rb:27:in `new'
    from (irb):1
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/railties-4.0.1/lib/rails/commands/console.rb:90:in `start'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/railties-4.0.1/lib/rails/commands/console.rb:9:in `start'
    from /Users/valentin/.rbenv/versions/1.9.3-p484/lib/ruby/gems/1.9.1/gems/railties-4.0.1/lib/rails/commands.rb:62:in `<top (required)>'
    from bin/rails:4:in `require'
    from bin/rails:4:in `<main>'