private com.google.protobuf.SingleFieldBuilderV3<
              com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankService,
              com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankService.Builder,
              com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankServiceOrBuilder>
          getRankServiceFieldBuilder() {
        if (rankServiceBuilder_ == null) {
          if (!(rankingConfigCase_ == 1)) {
            rankingConfig_ =
                com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankService
                    .getDefaultInstance();
          }
          rankServiceBuilder_ =
              new com.google.protobuf.SingleFieldBuilderV3<
                  com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankService,
                  com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankService.Builder,
                  com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankServiceOrBuilder>(
                  (com.google.cloud.vertexai.api.RagRetrievalConfig.Ranking.RankService)
                      rankingConfig_,
                  getParentForChildren(),
                  isClean());
          rankingConfig_ = null;
        }
        rankingConfigCase_ = 1;
        onChanged();
        return rankServiceBuilder_;
      }
<pre>
Optional. Config for Rank Service.
</pre>

<code>
.google.cloud.vertexai.v1.RagRetrievalConfig.Ranking.RankService rank_service = 1 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/RagRetrievalConfig.java