gistfile1.rb

class Person
  attr_writer :job
  
  def job
    @job || NoJob.new
  end
end

class Job
  def title
    "CEO"
  end
end

class NoJob
  def title
    raise "Person is unemployed"
  end
end

frank = Person.new
frank.job = Job.new
frank.job.title => "CEO"

bum = Person.new
bum.job.title => raises "Person is unemployed"