在Groovy中使用jsonbuilder修改json

我试图修改json的内容,然后打印它以查看它是否已更改此代码但收到错误

 def builder = new JsonBuilder(request)
 log.info(builder.content)
 builder.content.device.dpidsha1= 'abcd'  
 log.info(builder.toPrettyString())

错误:

no such property: device

json看起来像这样:

{
   "app":{ },
   "at":2,
   "badv":[ ],
   "bcat":[ ],
   "device":{
      "carrier":"310-410",
      "connectiontype":3,
      "devicetype":1,
      "dnt":0,
      "dpidmd5":"268d403db34e32c45869bb1401247af9",
      "dpidsha1":"1234",
.
.
}

有人可以帮助理解我做错了什么,我怎么能纠正它.