How can I avoid null using lambda in this case?

See more:

database

lambda

Spring

Java8

{
  "message": "The operation was successful.",
  "code": 200,
  "fileDetailResponseDtos": [
    {
      "phoneNumber": "550000000",
      "textMessage": "Message1",
      "createDateTime": "2021-10-20T15:45:27.277",
      "sender": "Anar",
      "status": 0,
      "originatry": 0
    },
    {
      "phoneNumber": "550000000",
      "textMessage": "Message2",
      "createDateTime": "2021-10-20T15:45:27.277",
      "sender": "Anar",
      "status": 0,
      "originatry": 0
    },
    {
      "phoneNumber": "550000000",
      "textMessage": "Message3",
      "createDateTime": "2021-10-20T15:45:27.277",
      "sender": "Anar",
      "status": 0,
      "originatry": 0
    }
  ]
}

However, when I perform an operation based on a phone number that is not in the database, it still returns the second part instead of this message.

{
  "message": "The operation was successful",
  "code": 200,
  "fileDetailResponseDtos": []
}

But I want it to look like this in the output.

{
  "message": "Unfortunately, no information was found for this number.",
  "code": 400,
}

Yes I know it's not possible to return a list null. Here is the method I wrote in the dao layer.

How can I output the message I want when I perform an invalid operation?

@Override
public List<FileDetail> getByPhoneNumberCBVersion(String phoneNumber) {
    CriteriaBuilder criteriaBuilder = entityManager.getCriteriaBuilder();
    CriteriaQuery<FileDetail> generateQueryWithMethods = criteriaBuilder.createQuery(FileDetail.class);
    Root<FileDetail> starsFrom = generateQueryWithMethods.from(FileDetail.class);
    generateQueryWithMethods.select(starsFrom);
    generateQueryWithMethods.where(criteriaBuilder.equal(starsFrom.get("phoneNumber"), phoneNumber));
    TypedQuery<FileDetail> query = entityManager.createQuery(generateQueryWithMethods);
    List<FileDetail> resultList = query.getResultList();
    return resultList;
}

What I have tried:

I tried to do something using lambda expressions a few times, but I couldn't do anything.