Spree::BaseHelper.module_eval do
  def display_price(product_or_variant,currency=nil)
    currency = if currency.nil? then Spree::Config[:presentation_currency] else currency end
    prices = product_or_variant.prices.select { |pr| pr.currency == currency }
    max_price = prices.max_by(&:price)
    min_price = prices.min_by(&:price)

    if !max_price || !min_price
      "재고가 없습니다"
    if max_price.price == min_price.price
      max_price.display_price.to_html
    else
      min_price.display_price.to_html + " ~ " + max_price.display_price.to_html
    end
  end
end

Spree::BaseHelper.module_eval do
  def display_price(product_or_variant,currency=nil)
    currency = if currency.nil? then Spree::Config[:presentation_currency] else currency end
    prices = product_or_variant.prices.select { |pr| pr.currency == currency }
    max_price = prices.max_by(&:price)
    min_price = prices.min_by(&:price)

    if max_price.price == min_price.price
      max_price.display_price.to_html
    else
      min_price.display_price.to_html + " ~ " + max_price.display_price.to_html
    end
  end
end

--- 
+++ 
@@ -5,6 +5,8 @@
     max_price = prices.max_by(&:price)
     min_price = prices.min_by(&:price)
 
+    if !max_price || !min_price
+      "재고가 없습니다"
     if max_price.price == min_price.price
       max_price.display_price.to_html
     else
Add "out of stock" error message if item doesn't have a max or min price
