我正在跟踪以下文档：https://www.elastic.co/guide/en/elasticsearch/reference/current/runtime-indexed.html
我有一个字段，我不想在运行时编写脚本，而是在索引时编写脚本，根据上面的内容，我可以简单地将该字段及其脚本像往常一样放在Map对象中。
下面是我尝试创建的索引的简化版本

{
  "settings": {
    "analysis": {
      "analyzer": {
        "case_insensitive_analyzer": {
          "type": "custom",
          "filter": ["lowercase"],
          "tokenizer": "keyword"
        }
      }
    }
  },
  "mappings": {
    "properties": {
      "id": {
        "type": "text"
      },
      "events": {
        "properties": {
          "fields": {
            "type": "text"
          },
          "id": {
            "type": "text"
          },
          "event": {
            "type": "text"
          },
          "time": {
            "type": "date"
          },
          "user": {
            "type": "text"
          },
          "state": {
            "type": "integer"
          }
        }
      },
      "eventLast": {
        "type": "date",
        "on_script_error": "fail",
        "script": {
          "source": "def events = doc['events']; emit(events[events.length-1].time.value"
        }
      }
    }
  }
}

我得到这个400错误：

{
    "error": {
        "root_cause": [
            {
                "type": "mapper_parsing_exception",
                "reason": "unknown parameter [script] on mapper [eventLast] of type [date]"
            }
        ],
        "type": "mapper_parsing_exception",
        "reason": "Failed to parse mapping [_doc]: unknown parameter [script] on mapper [eventLast] of type [date]",
        "caused_by": {
            "type": "mapper_parsing_exception",
            "reason": "unknown parameter [script] on mapper [eventLast] of type [date]"
        }
    },
    "status": 400
}

实际上，我正在尝试创建一个脚本化索引字段，该字段是根据文档的events数组中的最后一个事件时间计算出来的。
谢谢