{
  "type": "object",
  "required": ["closed_at", "merged_at", "closed_by", "merged_by"],
  "properties" : {
    "closed_at": { "type": ["datetime", "null"] },
    "merged_at": { "type": ["datetime", "null"] },
    "closed_by": {
      "oneOf": [
        { "type": "null" },
        { "$ref": "user.json" }
      ]
    },
    "merged_by": {
      "oneOf": [
        { "type": "null" },
        { "$ref": "user.json" }
      ]
    }
  },
  "additionalProperties": false
}