@java.lang.Override
  public com.google.cloud.vertexai.api.ContentOrBuilder getSystemInstructionOrBuilder() {
    return systemInstruction_ == null
        ? com.google.cloud.vertexai.api.Content.getDefaultInstance()
        : systemInstruction_;
  }
<pre>
Optional. Input only. Immutable. Developer set system instruction.
Currently, text only
</pre>

<code>
.google.cloud.vertexai.v1.Content system_instruction = 3 [(.google.api.field_behavior) = OPTIONAL, (.google.api.field_behavior) = IMMUTABLE, (.google.api.field_behavior) = INPUT_ONLY];
</code>
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/CachedContent.java