Elasticsearch search query: why params._source.nested_field.size() is not working in script?

问题

There are lot of questions and answers about this but still didn't get a satisfied answers. Elasticsearch version: 6.5

Index mapping

"_doc": {
    "properties": {
      "ssid": {
        "type": "long"
      },
      "nested_field": {
        "type": "nested"
      }
    }
  }
}

Search query:

{
  "query": {
    "bool": {
      "filter": {
        "script": {
          "script": "params._source.nested_field.size() > 1"
        }
      }
    }
  }
}

Also tried below query but no luck

{
  "query": {
    "bool": {
      "must": [
        {
          "nested": {
            "path": "nested_field",
            "query": {
              "bool": {
                "filter": {
                  "script": {
                    "script": "params._source.nested_field.size() > 1"
                  }
                }
              }
            }
          }
        }
      ]
    }
  }
}

Error

{
  "error": {
    "root_cause": [
      {
        "type": "script_exception",
        "reason": "runtime error",
        "script_stack": [
          "params._source.nested_field.size() > 1",
          "              ^---- HERE"
        ],
        "script": "params._source.nested_field.size() > 1",
        "lang": "painless"
      }
    ],
    "type": "search_phase_execution_exception",
    "reason": "all shards failed",
    "phase": "query",
    "grouped": true,
    "failed_shards": [
      {
        "shard": 0,
        "index": "testing_index",
        "node": "XXXXXXXXXXXXXXXXXXXXXXX",
        "reason": {
          "type": "script_exception",
          "reason": "runtime error",
          "script_stack": [
            "params._source.nested_field.size() > 1",
            "              ^---- HERE"
          ],
          "script": "params._source.nested_field.size() > 1",
          "lang": "painless",
          "caused_by": {
            "type": "null_pointer_exception",
            "reason": null
          }
        }
      }
    ]
  },
  "status": 500
}

params._source.nested_field return nested array while using in scripted_field but not working in validation query. Documentation are not complete about nested query with painless script.

来源：https://stackoverflow.com/questions/54022283/elasticsearch-search-query-why-params-source-nested-field-size-is-not-workin