Tell, don't ask

Before

The birth_year method is asking the user for her birthday and then getting the year, and if doesn't have one respond accordingly.

def birth_year(user)
  if user.birthday
    user.birthday.year
  else
    'No birthday year on file'
  end
end

Refactor

It should be telling the user to provide a birthday year and expect a coherent response if it has one or not.

def birth_year(user)
  user.birthday.year
end

class User
  def birthday
    @birthday || NullBirthday.new
  end
end

class NullBirthday
  def year
    'No birthday year on file'
  end
end