public ChatSession withSystemInstruction(Content systemInstruction) {
    return new ChatSession(
        model.withSystemInstruction(systemInstruction),
        history,
        previousHistorySize,
        Optional.of(rootChatSession.orElse(this)),
        automaticFunctionCallingResponder);
  }
Creates a copy of the current ChatSession with updated SystemInstruction.

@param systemInstruction a {@link com.google.cloud.vertexai.api.Content} containing system
    instructions.
@return a new {@link ChatSession} instance with the specified ToolConfigs.
java-vertexai/google-cloud-vertexai/src/main/java/com/google/cloud/vertexai/generativeai/ChatSession.java