I’ve a JSON:

[ {
  "Type" : "MOBILE_ADJUSTMENT",
  "MobileAdjustment" : {
    "BidModifier" : 110,
    "OperatingSystemType" : "IOS"
  },
  "DesktopAdjustment" : null,
  "SmartTvAdjustment" : null
} ]

I want to remove all nulls from it and also stay only Adjustment field. I tried with:

[
  {
    "operation": "default",
    "spec": {
      "*": {
        "*": "NULLS"
      }
    }
  },
  {
    "operation": "shift",
    "spec": {
      "*": {
        "*": {
          "NULLS": null,
          "*": {
            "@1": "&2"
          }
        }
      }
    }
  },
  {
    "operation": "default",
    "spec": {
      "AdGroupId": 1
    }
  },
  {
    "operation": "shift",
    "spec": {
      "*Adjustment": "&",
      "AdGroupId": "AdGroupId"
    }
  }
]

But it returns invalid result:

{
  "AdGroupId" : 1,
  "MobileAdjustment" : [ {
    "BidModifier" : 110,
    "OperatingSystemType" : "IOS"
  }, {
    "BidModifier" : 110,
    "OperatingSystemType" : "IOS"
  } ]
}

Somehow it builds array with two duplicates. How to fix that?
I expect:

{
   "AdGroupId":1,
   "MobileAdjustment":[
      {
         "BidModifier":110,
         "OperatingSystemType":"IOS"
      }
   ]
}