Bulk action user.update add to meeting is throwing an Error

[Elblinator]

Current behaviour:
If you try to add a participant via bulk action/multi action then the following Error is thrown:

Error: data.group_ids[1] must be integer

Payload:

[  {
    "action": "user.update",
    "data": [      {
        "id": 5097,
        "meeting_id": 101,
        "group_ids": [
          631,
          null  
        ]     
     }]
}]

Response:

{
    "success": false,
    "message": "data.group_ids[1] must be integer",
    "action_error_index": 0,
    "action_data_error_index": 0
}

Wanted behaviour:
It should be possible to add user via bulk action/multi select to one or more meetings,
if no group was specified then the default group should be used