Implementing the null object pattern on an ActiveRecord association. This is really a special case being represented with an object which acts like a null object.

nerd.rb

class Nerd < ActiveRecord::Base
  belongs_to :team, inverse_of: :nerds
  
  def team
    super || NullTeam.new
  end

end

null_team.rb

require 'active_model'

class NullTeam
  extend  ActiveModel::Naming
  include ActiveModel::Conversion

  def self.model_name
    Team.model_name
  end

  def lead
    nil
  end

  def lead_id
    nil
  end

  def name
    'No team'
  end

  def persisted?
    false
  end

  def blank?
    true
  end

  def present?
    !blank?
  end
end

This could likely be simplified by relying on ActiveModel::Model which did not exist when I originally created this NullTeam.