null_object.rb

class Config
  def self.email_enabled? ; ... ; end
  def self.emailer ; if has_amiko? then Amiko else MailerMonkey end ; end
end
def advertise_discount_for_movie
  if Config.email_enabled?
    moviegoers = Moviegoer.interested_in(params[:movie_id])
    EmailList.new(Config.emailer).send_email_to(moviegoers)
  end
end