Kibana Watcher: Aggregation not working if only one hit by query

Question

I have the following kibana watcher with aggregation of the results:

"aggs": {
            "group_by_ip": {
              "multi_terms": {
                "terms": [
                  {
                    "field": "request"
                  },
                  {
                    "field": "Message"
                  },
                  {
                    "field": "applicationcluster“
                  }
                ]
              }
            }

If the query returns only one hit, the aggregation bucket seems to be empty.

"result": {
    "execution_time": "2024-03-22T10:44:25.407Z",
    "execution_duration": 775,
    "input": {
      "type": "search",
      "status": "success",
      "payload": {
        "_shards": {
          "total": 3,
          "failed": 0,
          "successful": 3,
          "skipped": 0
        },
        "hits": {
          "hits": [],
          "total": 1,
          "max_score": null
        },
        "took": 17,
        "timed_out": false,
        "aggregations": {
          "group_by_ip": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": []
          }
        }
      }

Is there any way to perform the aggregation even if there´s only one hit? Thanks!

Executing the watcher and aggregation works with one single hit.