## Mapping
"categories": {
  "type": "nested",
  "properties": {
    "id": {
      "type": "long"
    },
    "name": {
      "type": "keyword"
    }
  }
}
## Search
GET development_tasks_index/_search
{
  "query": {
    "bool": {
      "must": {
        "match_all": {}
      }
    }
  },
  "aggs": {
    "categories": {
      "nested": {
        "path": "categories"
      }
    }
  }
}

## result
"aggregations": {
  "categories": {
    "doc_count": 4
  }
}

## Expectation
"aggregations": {
  "categories": {
    "doc_count": 4,
    "id": 11,
    "name": "Category ABC"
  }
}