MarkUiInitialData.json

{
  "id": 1,
  "name": "1. Semester",
  "validFrom": "2017-01-01",
  "validTo": "2017-06-30",
  "subjects": [
    {
      "id": 1,
      "name": "Math",
      "color": "...",
      "parentMarkGroup": {
        "id": 1,
        "value": 5.5,
        "weight": 1.0,
        "marks": [
          {
            "id": 1,
            "value": 5.0,
            "weight": 2.0,
          }
        ],
        "markGroups": [
          {
            "id": 1,
            "value": 5.5,
            "weight": 1.0,
            "marks": [
              {
                "id": 1,
                "value": 5.0,
                "weight: 2.0,
              }
            ]
          }
        ]
      }
    }
  ]
}      

Line 20 add markGroupId

line 34 will contain an empty list with netsted groups