再用ElasticSearch的collapse搜索时出现：only keywords and numbers are accepted

查询字段：
{
  "query": {
    "match": {
      "language": "CN"
    }
  },
  "collapse": {
    "field": "client_id"
  }
}
 
错误
"root_cause": [
            {
                "type": "search_context_exception",
                "reason": "unknown type for collapse field `client_id`, only keywords and numbers are accepted"
            }
        ],