无效的聚合路径 (invalid_aggregation_path_exception) 错误排查与解决

GET /<index>/_search
{
  "aggs": {
    "level1": {
      "terms": { "field": "field.keyword" },
      "aggs": {
        "level2": {
          "avg": { "field": "value" }
        }
      }
    }
  }
}