In checking the error code, you probably ought to check for code 4. I believe Code 4 means no file was uploaded, and there are many instances where that's perfectly OK.
Such as when you have a form with multiple data items, including file and image uploads, plus whatever else. The user might not be adding a new upload for whatever reason, such as there may already be a file in the system from an earlier update, and the user is satisfied with that.