How to check for empty GUID

Question

I have in database a empty GUID.

 

But if I execute this code:

List listOfOneResource = await _resourceService.GetResourcesById(new List { new Guid(welcome.WelcomePopupImage) });
Guid fileId = listOfOneResource.First().FileId ?? Guid.Empty; // this should never be empty in case of an image type resource
string fileIdString = fileId.ToString();
welcome.WelcomePopupImage = _appSettings.MedicalBaseUrl + "/resources/image/" + fileIdString + ".jpg";

I get an error on this line:

List listOfOneResource = await _resourceService.GetResourcesById(new List { new Guid(welcome.WelcomePopupImage) });

"message": "Unrecognized Guid format.", 

 

So what I have to change?