如何在空日期项目上映射哈希数组并输出0？

I have an array of hashes:

我有一系列哈希：

items = [
   {:created=>"2013-12-01", :amount=>16611},
   {:created=>"2013-12-02", :amount=>16611}, 
   {:created=>"2013-12-04", :amount=>9428},
   {:created=>"2013-12-05", :amount=>11628},
   {:created=>"2013-12-06", :amount=>4600},
   {:created=>"2013-12-09", :amount=>21756},
   {:created=>"2013-12-10", :amount=>18127}
]
items =