I have an Elasticsearch index, part of it is as follows:

...
},
                "entity": {
                    "properties": {
                        "DateTime": {
                            "type": "date"
                        },
                        "Event": {
                            "type": "keyword"
                        },
                        "Location": {
                            "type": "keyword"
                        },
                        "Organ": {
                            "type": "keyword"
                        },
                        "Person": {
                            "type": "keyword"
                        }
                    }
                },
...

I want to find the most frequent person. So, I query the index in the following ways:

{"size":0, "query":{"match_all":{}},"aggs":{"top_locations":{"terms":{"field":"entity.Person","size":1}}}}

and

{"size":0, "query":{"match_all":{}},"aggs":{"top_locations":{"terms":{"field":"entity.Person.keyword","size":1}}}}

The problem is that the first query works fine, but the second does not work.