ElasticSearch在访问脚本字段中的参数[“源”]时返回空的_指针_异常

GET /users/_search
{
  "query": {
    "function_score": {
        "query" : {
          "match_all": {}
        },
        "score_mode" : "sum",
        "boost_mode" : "sum",
        "script_score": {
          "script": {
            "lang": "painless",
            "source": "params['_source']"
          }
        }
      }
    }
  }

  {
"shard": 0,
"index": "users",
"node": "xxxxxxxxxxxxxxxxxxx",
"reason": {
  "type": "script_exception",
  "reason": "runtime error",
  "script_stack": [
    "params._source",
    "      ^---- HERE"
  ],
  "script": "params._source",
  "lang": "painless",
  "caused_by": {
    "type": "null_pointer_exception",
    "reason": null
  }
}