private void ensureToolsIsMutable() {
      if (!((bitField0_ & 0x00000020) != 0)) {
        tools_ = new java.util.ArrayList<com.google.cloud.vertexai.api.Tool>(tools_);
        bitField0_ |= 0x00000020;
      }
    }
<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