[java high level client 7.9.1] highlight in inner hit is null

I want to get highlight data in inner hit.
in response, but, highlight in inner hit is null.
did I miss something?

portion of class file:

//-- innerHit's Highlight
HighlightBuilder enHighlightBuilder = new HighlightBuilder();
enHighlightBuilder.field("content_en.text");

//-- innerHit's Source
String[] enIncludes = {"content_en.page", "content_en.text"};
FetchSourceContext enFetchSourceContext = new FetchSourceContext(true, enIncludes, new String[0]);

//-- innerHit setting
InnerHitBuilder enInnerHitBuilder = new InnerHitBuilder();
enInnerHitBuilder.setHighlightBuilder(enHighlightBuilder);
enInnerHitBuilder.setFetchSourceContext(enFetchSourceContext);

//-- final query
BoolQueryBuilder queryBuilder = new BoolQueryBuilder();
queryBuilder.should(
    QueryBuilders.nestedQuery(
            "content_en"
            , QueryBuilders.queryStringQuery(keyword)
                .defaultField("content_en.text")
                .analyzer("en_analyzer")
            , ScoreMode.None
        ).innerHit(enInnerHitBuilder)
    );
sourceBuilder.query(queryBuilder);

SearchRequest searchReq = new SearchRequest();
searchReq.indices(indice);
searchReq.source(sourceBuilder);

//-- response
List<Map<String, Object>> searchResult = new ArrayList<Map<String, Object>>();
SearchResponse response = client.search(searchReq, RequestOptions.DEFAULT);
SearchHits hits = response.getHits();

for (SearchHit hit : hits) {
    Map<String, SearchHits> innerHits = hit.getInnerHits();
    SearchHits enInnerHits = innerHits.get("content_en");
        
    Map<String, HighlightField> highMap = enInnerHit.getHighlightFields();
}

mapping:

    {
      "test-doc" : {
        "mappings" : {
          "properties" : {
            "content" : {
              "type" : "text"
            },
            "content_en" : {
              "type" : "nested",
              "properties" : {
                "page" : {
                  "type" : "integer"
                },
                "text" : {
                  "type" : "text",
                  "analyzer" : "en_analyzer"
                }
              }
            },
            "content_lang" : {
              "type" : "keyword"
            },
            "convert_nm" : {
              "type" : "keyword"
            },
            "ext" : {
              "type" : "keyword"
            },
            "file_nm" : {
              "type" : "keyword"
            },
            "file_size" : {
              "type" : "long"
            },
            "upload_date" : {
              "type" : "date",
              "format" : "[yyyy-MM-dd HH:mm:ss.SSS]"
            },
            "uploader" : {
              "type" : "keyword"
            },
            "use_yn" : {
              "type" : "boolean"
            }
          }
        }
      }
    }

I found problem.
problem is analyzer, not inner hit highlight.