topics dashboard drop-down empty

[Sharofiddin]

topics.json generated dashboard has a dropdown to filter topics in namespace, and it generated like this:

      {    
        "allValue": null,
        "current": {},
        "datasource": "standalone",
        "hide": 0,
        "includeAll": true,
        "label": "Topic",
        "multi": false,
        "name": "topic",
        "options": [],
        "query": "pulsar_topics_count{topic=~\".+\"}",
        "refresh": 2,
        "regex": "/.*topic=\\\"([^\\\"]+)\\\".*/",
        "sort": 1,
        "tagValuesQuery": "",
        "tags": [],
        "tagsQuery": "",
        "type": "query",
        "useTags": false
      }

But pulsar_topics_count actually has no field "topic", for example:

pulsar_topics_count{cluster="standalone", instance="localhost:8080", job="proxy", namespace="public/functions"}

there is no topic field and dropdown wont show anything.