Suggester template Search issue ElasticSearch

Question

I am using the below gradle implementation 'co.elastic.clients:elasticsearch-java:8.1.0'

I am having a script posted in elasticsearch as below

{
  "script": {
    "lang": "mustache",
    "source": {
      "suggest": {
        "text": "{{query_string}}",
        "simple_phrase": {
          "phrase": {
            "field": "title.completion",
            "size": 1,
            "direct_generator": [
              {
                "field": "title.completion",
                "size": 4,
                "suggest_mode": "popular",
                "max_edits": 1,
                "prefix_length": 3
              }
            ],
            "collate": {
              "query": {
                "source": {
                  "match": {
                    "{{field_name}}": "{{suggestion}}"
                  }
                }
              },
              "params": {
                "field_name": "title"
              },
              "prune": true
            }
          }
        }
      }
    },
    "params": {
      "query_string": "My query string"
    }
  }
}

When i run the above suggestor i get results as below:

{
  "took": 5,
  "timed_out": false,
  "_shards": {
    "total": 3,
    "successful": 3,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": {
      "value": 0,
      "relation": "eq"
    },
    "max_score": null,
    "hits": []
  },
  "suggest": {
    "simple_phrase": [
      {
        "text": "abd",
        "offset": 0,
        "length": 6,
        "options": [
          {
            "text": "abc",
            "score": 0.0018216542,
            "collate_match": true
          }
        ]
      }
    ]
  }
}

I am using the below code to do a template search

SearchTemplateRequest request = new SearchTemplateRequest.Builder()
                    .index(index)
                    .id("xyz")
                    .params("query_string", JsonData.of(queryName))
                    .build();

SearchTemplateResponse searchTemplateResponse = elasticNewSearchClient.searchTemplate(request, MyElasticSearchIndexFieldsClassSerialized.class);

MyElasticSearchIndexFieldsClassSerialized class contains all the fields of the index and it implements Serialized

When i am running this, i am getting the below error

Method threw co.elastic.clients.json.UnexpectedJsonEventException Exception