public Builder clearSource() {
      sourceCase_ = 0;
      source_ = null;
      onChanged();
      return this;
    }
<pre>
Defines a retrieval tool that model can call to access external knowledge.
</pre>

Protobuf type {@code google.cloud.vertexai.v1.Retrieval}
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/Retrieval.java