null_pattern_9.rb

class GuaranteedProduct
  def self.find(id)
    Product.find(id) || MissingProduct.new
  end
end

product_ids = [123,456,'',789]
products = product_ids.map{|id| GuaranteedProduct.find(id)}
=> [#<Product:0x000123123 @name="TV"..>, 
    #<Product:0x000123124 @name="Cellphone"..>,
    #<MissingProduct:>,
    #<Product:0x000123125 @name="iPad"..>
  ]
  
products.each do |product|
  puts product.name
end
# "TV"
# "Cellphone"
# "no product"
# "iPad"