Query for a grafana variable does not return values

Grafana Configuration
1

Trying to query elastic data and create a a variable in grafana for dashboarding, but it doesn’t populate the values in the preview section. Here is the JSON msg format in source data (Elastic v7.5):

Variable query in grafana:
{“find”: “terms”, “field”: “agent.hostname”}

No preview data comes up.

However, when I chose {“find”: “terms”, “field”: “jvm”} - I see data being previewed.

Appreciate any insights into it…

Sample source data in elastic:

{
  "_index": "elastic-2020.09.30",
  "_type": "_doc",
  "_id": "O69R4HQBkDz3L01E8RLR",
  "_version": 1,
  "_score": null,
  "_source": {
    "tenurefree": 405913392,
    "@timestamp": "2020-09-30T18:41:39.712Z",
    "ecs": {
      "version": "1.1.0"
    },
    "tags": [
      "beats_input_codec_plain_applied"
    ],
    "jvm": "xyz",
    "log": {
      "file": {
        "path": "log.xml.013"
      },
      "offset": 9884781,
      "flags": [
        "multiline"
      ]
    },
    "durationms": 13.794,
    "agent": {
      "type": "filebeat",
      "ephemeral_id": "a6a86b85-0ae0-441a-b85c-4aeae3ff7ccb",
      "hostname": "xyz",
      "id": "ff3ddde2-9b11-414f-a6db-a8ddd09d74f8",
      "version": "7.5"
    }
  },
  "fields": {
    "@timestamp": [
      "2020-09-30T18:41:39.712Z"
    ]
  },
  "sort": [
    1601491299712
  ]
}

Source data is being ingested into elastic through a template, where the agent.hostname is being captured as a type text.

  "agent.hostname" : {
      "type" : "text",
      "fields" : {
        "keyword" : {
          "type" : "keyword"
        }
      }