如何计算无 - 在Rails上无

Rails 4，Spree 2.1

The Issue:

使用Spree Flexi Variants雕刻计算器将项目添加到购物车时，出现错误：

undefined method `value' for nil:NilClass

我的雕刻计算器模型中的这条线是否会导致此错误？

def compute(product_customization, variant=nil)
  return 0 unless valid_configuration? product_customization

  # expecting only one CustomizedProductOption
  opt = product_customization.customized_product_options.detect {|cpo| cpo.customizable_product_option.name == "inscription" } rescue ''
  opt.value.length * (preferred_price_per_letter || 0)
end

def valid_configuration?(product_customization)
  true
end

至于 Value 方法，有什么想法吗？

我已经尝试过定义 Value ，但似乎没有任何效果 . 我有另一个名为金额时间的计算器 . 设置方式几乎相同;但是，这一个有效 . 在我的截止日期之前遇到困惑和方式 .

Here is the github repo with the branch that I am using: https://github.com/jsqu99/spree_flexi_variants/tree/spree-2-1-wip

Trace:

NoMethodError (undefined method `value' for nil:NilClass)
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/calculator/engraving.rb:29:in `compute'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/product_customization.rb:11:in `price'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_contents_decorator.rb:32:in `block in add_to_line_item'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_contents_decorator.rb:32:in `map'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_contents_decorator.rb:32:in `add_to_line_item'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_contents_decorator.rb:7:in `add'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_populator_decorator.rb:36:in `attempt_cart_add'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_populator_decorator.rb:17:in `block in populate'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_populator_decorator.rb:16:in `each'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/models/spree/order_populator_decorator.rb:16:in `populate'
/Users/russellkompinski/Desktop/spree_commerce/spree_flexi_variants/app/controllers/spree/orders_controller_decorator.rb:18:in `populate'