[
  {
    "id": "$addFields example",
    "stage": "$addFields",
    "kind": "example",
    "pipeline": [
      {
        "$addFields": {
          "total": {
            "$multiply": [
              "$quantity",
              "$price"
            ]
          }
        }
      }
    ],
    "input": [
      {
        "quantity": 2,
        "price": 5,
        "orderId": "A"
      }
    ],
    "result": [
      {
        "quantity": 2,
        "price": 5,
        "orderId": "A",
        "total": 10.0
      }
    ]
  },
  {
    "id": "$addFields empty input",
    "stage": "$addFields",
    "kind": "empty input",
    "pipeline": [
      {
        "$addFields": {
          "total": {
            "$multiply": [
              "$quantity",
              "$price"
            ]
          }
        }
      }
    ],
    "input": [],
    "result": []
  },
  {
    "id": "$addFields invalid specification",
    "stage": "$addFields",
    "kind": "invalid specification",
    "pipeline": [
      {
        "$addFields": null
      }
    ],
    "input": [
      {
        "quantity": 2,
        "price": 5,
        "orderId": "A"
      }
    ],
    "error": "IllegalArgumentException",
    "message": "$addFields stage requires an object"
  },
  {
    "id": "$addFields null and missing source",
    "stage": "$addFields",
    "kind": "null and missing source",
    "pipeline": [
      {
        "$addFields": {
          "copy": "$value"
        }
      }
    ],
    "input": [
      {},
      {
        "value": null
      }
    ],
    "result": [
      {
        "copy": null
      },
      {
        "value": null,
        "copy": null
      }
    ]
  }
]