Bucket script pipeline aggregation under a single bucket aggregation produces a class cast exception

[iverase]

Adding a bucket script pipeline aggregation under a single buckets aggregation like the filter aggregation results on a class class exception, for example:

POST test/_doc 
{
  "field" : "foo"
}

GET test/_search 
{
  "size": 0,
  "aggs": {
    "single_bucket": {
      "filter": {
        "exists": {
          "field": "field.keyword"
        }
      },
      "aggs": {
        "value" : {
          "cardinality": {
            "field": "field.keyword"
          }
        },
        "bucket_script": {
          "bucket_script": {
            "buckets_path": {
              "card" : "value"
            },
            "script": "params.card + 1"
          }
        }
      }
    }
  }
}

Output:

{
  "error": {
    "root_cause": [],
    "type": "search_phase_execution_exception",
    "reason": "",
    "phase": "rank-feature",
    "grouped": true,
    "failed_shards": [],
    "caused_by": {
      "type": "class_cast_exception",
      "reason": "class org.elasticsearch.search.aggregations.bucket.filter.InternalFilter cannot be cast to class org.elasticsearch.search.aggregations.InternalMultiBucketAggregation (org.elasticsearch.search.aggregations.bucket.filter.InternalFilter and org.elasticsearch.search.aggregations.InternalMultiBucketAggregation are in module org.elasticsearch.server@8.17.0 of loader 'app')"
    }
  },
  "status": 500
}

[elasticsearchmachine]

Pinging @elastic/es-analytical-engine (Team:Analytics)