已尝试执行以下查询以获取2个数组字段的值及其对应的长度，但数组值和长度不匹配。

查询：

GET my_index/_search
{
  "_source": ["file_types", "link_to_file"],
  "query": {
    "bool": {
      "filter": [
        {
          "term": {
            "_id": "45t8724b811b590d54cc1925166a9cb5"
          }
        }
      ]
    }
  },
  "script_fields": {
    "file_types_len": {
      "script": "doc['file_types'].length"
    },
    "link_to_file_len": {
      "script": "doc['link_to_file'].length"
    }
  }
}

结果：

{
  "_index": "my_index-150522",
  "_type": "_doc",
  "_id": "45t8724b811b590d54cc1925166a9cb5",
  "_score": 0.0,
  "_source": {
    "link_to_file": [
      "https://bucket.s3.amazonaws.com/abc123",
      "https://bucket.s3.amazonaws.com/wer134"
    ],
    "file_types": ["jpeg", "jpeg"]
  },
  "fields": {
    "file_types_len": [1],
    "link_to_file_len": [2]
  }
}

根据返回的值，两个数组的长度都是2，但其中一个数组的长度是1。为什么会这样？