error when using translate function

I'm using this Model

export interface QuestionsToAnswerToResponse {
  // the language of the improved reply
  questionsToAnswerTo:
    | UnknownText
    | [
        {
          // The question to ask the user to answer
          question: string;
          // The question type, default is text
          answerType: "text" | "number" | "date" | "radio" | "checkbox";
          // The question options if the question type is radio or checkbox otherwwise set to null
          answerOptions: string[] | null;
        }
      ];
}

export interface UnknownText {
  type: "unknown";
  text: string; // The text that wasn't understood
}

const model = createLanguageModel(process.env);
export const getQuestions = async (
  mails: string,
  context: Context
): Promise<Success<QuestionsToAnswerToResponse>> => {
  let schema;
  try {
    schema = fs.readFileSync(
      path.join(__dirname, "/questionsToanswerModel.ts"),
      "utf8"
    );
  } catch (error) {
    context.log("fileread", { error });
  }
  let translator;
  context.log("summariz");
  translator = createJsonTranslator<QuestionsToAnswerToResponse>(
    model,
    schema,
    "QuestionsToAnswerToResponse"
  );
  context.log("typechat");
  return new Promise(async (resolve, reject) => {
    let response: Success<QuestionsToAnswerToResponse>;
    try {
      response = await translator.translate(`${mails}`);
      context.log("response typechat", response);
    } catch (error) {
      context.log("response typechat error");
      context.log({ error });
      return reject(error);
    }
    if (!response.success) {
      context.log(response);
      return reject(response);
    }
    resolve(response);
  });
};

I'm getting this error when I use translate function :

"JSON validation failed: Type '{ question: string; answerType: string; answerOptions: null; }' is not assignable to type 'undefined'.\nType '{ question: string; answerType: string; answerOptions: null; }' is not assignable to type 'undefined'.\nType '{ question: string; answerType: string; answerOptions: null; }' is not assignable to type 'undefined'.\nType '{ question: string; answerType: string; answerOptions: null; }' is not assignable to type 'undefined'.\n{\n \"questionsToAnswerTo\": [\n {\n \"question\": \"What is the add-in name?\",\n \"answerType\": \"text\",\n \"answerOptions\": null\n },\n {\n \"question\": \"Where can the add-in be found?\",\n \"answerType\": \"text\",\n \"answerOptions\": null\n },\n {\n \"question\": \"What is the link to the support document?\",\n \"answerType\": \"text\",\n \"answerOptions\": null\n },\n {\n \"question\": \"What is the link to the privacy statement?\",\n \"answerType\": \"text\",\n \"answerOptions\": null\n },\n {\n \"question\": \"What are the links to Your Services & Add-ins, Microsoft AppSource, and Get Help?\",\n \"answerType\": \"text\",\n \"answerOptions\": null\n }\n ]\n}"

Start with the QuestionsToAnswerToResponse model in questionsToanswerModel.ts and the createJsonTranslator call that invokes translate. Reproduce the JSON validation failure using the supplied model and response, then trace how the union and array types are validated. Done means the reported valid response is accepted or the issue clearly documents the model constraint causing rejection.