Can not access to params._source in script_score

[wgkoro]

Hi. newbie here.
I'm trying to write script_score with params._source, but it returns null pointer exception.
(I want to access nested data)
Query is like this.

GET /users/_search
{
  "query": {
    "function_score": {
        "query" : {
          "match_all": {}
        },
        "score_mode" : "sum",
        "boost_mode" : "sum",
        "script_score": {
          "script": {
            "lang": "painless",
            "source": "if (params._source['categories'][0]['category_id'] == 3) { 10 } else { -50 }"
          }
        }
      }
    }
  }

It returns

{
  "error": {
    "root_cause": [
      {
        "type": "script_exception",
        "reason": "runtime error",
        "script_stack": [
          "if (params._source['categories'][0]['category_id'] == 3) { ",
          "          ^---- HERE"
        ],
        "script": "if (params._source['categories'][0]['category_id'] == 3) { 10 } else { -50 }",
        "lang": "painless"
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "users",
        "node": "xxxxxxxxxxxxxxxxx(filtered)",
        "reason": {
          "type": "script_exception",
          "reason": "runtime error",
          "script_stack": [
            "if (params._source['categories'][0]['category_id'] == 3) { ",
            "          ^---- HERE"
          ],
          "script": "if (params._source['categories'][0]['category_id'] == 3) { 10 } else { -50 }",
          "lang": "painless",
          "caused_by": {
            "type": "null_pointer_exception",
            "reason": null
          }
        }
      }
    ]
  },
  "status": 500
}

How can I access params['_source'] in script_score?
※ Elasticsearch version ... 6.4.2

params.containsKey('_source') returns false, params.isEmpty() returns true ...

[wgkoro]

In local machine,
I tried with version 6.3.2 => No errors
version 6.4.2 => Error

Does 6.4.x changed something around "params"?

[rjernst (Ryan Ernst)]

In this particular case, the issue is an unintentional side effect of refactoring. However, it does fall in line with long suggested guidance, which is accessing _source in scoring scripts is slow and should not be done.

Do you have doc values disabled for categories and category_id?

[wgkoro]

Thank you for reply.

the issue is an unintentional side effect of refactoring

Oh I see..

Do you have doc values disabled for categories and category_id?

Now not.I have to find alternative.