Unable to do a nested query on saved objects using KQL

[mikecote]

I'm having a hard time creating a nested query with KQL using the saved objects API. I keep getting a This key 'actionTypeId' need to be wrapped by a saved object type like alert: error on the nested query.

Steps to reproduce:

1. Enable alerting in your kibana.yml config xpack.actions.enabled: true and xpack.alerting.enabled: true.
2. Adjust and run following curl command curl -X GET 'http://elastic:changeme@localhost:5603/api/saved_objects/_find?type=alert&filter=alert.attributes.actions%3A%7B%20actionTypeId%3A%20%22.server-log%22%20%7D'.
3. Note error returned from API.

Saved object mapping:

{
  "alert": {
    "properties": {
      ...
      "actions": {
        "type": "nested",
        "properties": {
          "group": {
            "type": "keyword"
          },
          "actionRef": {
            "type": "keyword"
          },
          "actionTypeId": {
            "type": "keyword"
          },
          "params": {
            "enabled": false,
            "type": "object"
          }
        }
      }
    }
  }
}

GET /api/saved_objects/_find query:

{
  type: 'alert',
  filter: 'alert.attributes.actions:{ actionTypeId: ".server-log" }',
}

Error message:

{"message":"This key 'actionTypeId' need to be wrapped by a saved object type like alert: Bad Request","statusCode":400,"error":"Bad Request"}

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[mikecote]

Solved by #51847, thank you @XavierM for looking into this!