public Builder setSystemInstruction(
        com.google.cloud.vertexai.api.Content.Builder builderForValue) {
      if (systemInstructionBuilder_ == null) {
        systemInstruction_ = builderForValue.build();
      } else {
        systemInstructionBuilder_.setMessage(builderForValue.build());
      }
      bitField0_ |= 0x00000010;
      onChanged();
      return this;
    }
<pre>
Optional. The user provided system instructions for the model.
Note: only text should be used in parts and content in each part will be in
a separate paragraph.
</pre>

<code>
optional .google.cloud.vertexai.v1.Content system_instruction = 5 [(.google.api.field_behavior) = OPTIONAL];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/CountTokensRequest.java