n3example.rb

# app/domain/null_account.rb
class NullAccount

  def id
    raise "You are calling id on an account that doesn't exist. Make sure the user you're working with has accounts first before trying to call them."
  end
  
  def available_balance
    Money.new(available_balance_cents, available_balance_currency)
  end
  
  def available_balance_cents
    0
  end
  
  def available_balance_currency
    "CAD"
  end
  
  def valid?
    false
  end
  
  def present?
    false
  end
  
  def blank?
    true
  end
  
  def account_key
    raise "account_key is being called on a NullAccount!!"
  end
  
  def currency
    "CAD"
  end
  
  def save
    raise ActiveRecord::RecordInvalid
  end
  
  def update
    raise ActiveRecord::RecordInvalid
  end
end