Elasticsearch terms facet string

terms_facet_fail

$ curl -XPOST localhost:9200/test/test/ -d '{"timestamp": "random_date", "tag":"blue", "counter": "5"}'
{"ok":true,"_index":"test","_type":"test","_id":"qVmyc9otSqWqUOKWoteM5Q","_version":1}

$ curl -XGET localhost:9200/test/test/_mapping?pretty=true
{
  "test" : {
    "properties" : {
      "counter" : {
        "type" : "string"
      },
      "tag" : {
        "type" : "string"
      },
      "timestamp" : {
        "type" : "string"
      }
    }
  }
}

$ curl -XPOST localhost:9200/test/test/_search?pretty=true -d '{
>     "query": {
>         "match_all": {}
>     },
>     "facets" : {
>         "test_facet" : {
>             "terms_stats" : {
>                 "key_field" : "tag",
>                 "value_field" : "counter"
>             }
>         }
>     }
> }'
{
  "error" : "SearchPhaseExecutionException[Failed to execute phase [query_fetch], total failure; shardFailures {[tbpy27tVRIeA5qjVsI-a4Q][test][0]: QueryPhaseExecutionException[[test][0]: query[ConstantScore(NotDeleted(cache(_type:test)))],from[0],size[10]: Query Failed [Failed to execute main query]]; nested: ClassCastException[org.elasticsearch.index.field.data.strings.SingleValueStringFieldData cannot be cast to org.elasticsearch.index.field.data.NumericFieldData]; }]",
  "status" : 500
}