null_object.rb

null_object.rb

class Seller
  belongs_to :user
  
  def can_add_products?
    products.count < seller.products_limit
  end
  
  def seller
    if is_sysadmin?
      NullSeller.new
    else
      super
    end
  end
end

class User
  has_one :seller
end

# Usage

if user.seller.can_add_products?
  puts "Can add products"
end