private com.google.protobuf.SingleFieldBuilderV3<
            com.google.cloud.vertexai.api.RetrievalConfig,
            com.google.cloud.vertexai.api.RetrievalConfig.Builder,
            com.google.cloud.vertexai.api.RetrievalConfigOrBuilder>
        getRetrievalConfigFieldBuilder() {
      if (retrievalConfigBuilder_ == null) {
        retrievalConfigBuilder_ =
            new com.google.protobuf.SingleFieldBuilderV3<
                com.google.cloud.vertexai.api.RetrievalConfig,
                com.google.cloud.vertexai.api.RetrievalConfig.Builder,
                com.google.cloud.vertexai.api.RetrievalConfigOrBuilder>(
                getRetrievalConfig(), getParentForChildren(), isClean());
        retrievalConfig_ = null;
      }
      return retrievalConfigBuilder_;
    }
<pre>
Optional. Retrieval config.
</pre>

<code>
.google.cloud.vertexai.v1.RetrievalConfig retrieval_config = 2 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/ToolConfig.java