Terms aggregation filtered the length of terms

gistfile1.txt

DELETE /filtered_aggs

PUT /filtered_aggs

PUT /filtered_aggs/example/1
{
  "text" : "this is test doc"
}

PUT /filtered_aggs/example/2
{
  "text" : "elasticsearch is fantastic open source"
}

GET /filtered_aggs/_search


GET /filtered_aggs/_search
{
  "aggs": {
    "term_count": {
      "terms": {
        "field": "text",
        "script": "_value.length() > 2 ? _value : ''", 
        "size": 10
      }
    }
  }
}

## output sample
{
   "took": 13,
   "timed_out": false,
   "_shards": {
      "total": 5,
      "successful": 5,
      "failed": 0
   },
   "hits": {
      "total": 2,
      "max_score": 1,
      "hits": [
         {
            "_index": "filtered_aggs",
            "_type": "example",
            "_id": "1",
            "_score": 1,
            "_source": {
               "text": "this is test doc"
            }
         },
         {
            "_index": "filtered_aggs",
            "_type": "example",
            "_id": "2",
            "_score": 1,
            "_source": {
               "text": "elasticsearch is fantastic open source"
            }
         }
      ]
   },
   "aggregations": {
      "term_count": {
         "doc_count_error_upper_bound": 0,
         "sum_other_doc_count": 0,
         "buckets": [
            {
               "key": "is",
               "doc_count": 2
            },
            {
               "key": "doc",
               "doc_count": 1
            },
            {
               "key": "elasticsearch",
               "doc_count": 1
            },
            {
               "key": "fantastic",
               "doc_count": 1
            },
            {
               "key": "open",
               "doc_count": 1
            },
            {
               "key": "source",
               "doc_count": 1
            },
            {
               "key": "test",
               "doc_count": 1
            },
            {
               "key": "this",
               "doc_count": 1
            }
         ]
      }
   }
}