Error when claiming

WHen i press  /claim i have this error:

10/28 00:19:11 | NullReferenceException: Object reference not set to an instance of an object

My cnfig is this:     "Normal Rewards": {
      "Normal Rewards Enabled?": true,
      "Rewards List": {
        "@": [
          "giveto {steamID} scrap 25"
        ],
        "@6": [
          "giveto {steamID} diesel_barrel"
        ],
        "@12": [
          "giveto {steamID} supply.signal 1"
        ],
        "first": [
          "giveto {steamID} xmas.present.medium"
        ]
      }
    }