Why does FaceAttributes.Gender return null?

Question

API

I don't know, maybe someone dealt with microsoft face api. The problem is that the Gender property of the FaceAttributes class instance returns null, while the photo is recognized normally on the site.
Method:

private async Task<FaceAttributes[]> UploadAndDetectFaces(string imageFilePath)
        {
            try
            {
                using (Stream imageFileStream = File.OpenRead(imageFilePath))
                {
                    var faces = await faceServiceClient.DetectAsync(imageFileStream);
                    var faceRects = faces.Select(face => face.FaceAttributes);
                    return faceRects.ToArray();
                }
            }
            catch (Exception)
            {
                return new FaceAttributes[0];
            }
        }

Call:

FaceAttributes[] faceAttributes;

            for (int i = 0; i < fileNames.Length; i++) 
            {
                StatusLabel.StringValue = string.Format("{0} из {1} ({2})", i + 1, fileNames.Length, fileNames[i]);

                faceAttributes = await UploadAndDetectFaces(fileNames[i]);
                try{
                    if (faceAttributes.Length != 0)
                    {
                        if(faceAttributes.Length > 1)
                        {
                            File.Move(fileNames[i], endDir + "/Couple/" + fileNames[0].Substring(fileNames[0].LastIndexOf('/') + 1));
                            if(File.Exists(fileNames[i]))
                                File.Delete(fileNames[i]);
                        }
                        else
                        {                            
                            if(faceAttributes[0]?.Gender == "male")// Это условия пропускается из-за того, что Gender = null 
                            {
                                File.Move(fileNames[i], endDir + "/Men/" + fileNames[0].Substring(fileNames[0].LastIndexOf('/') + 1));
                                if(File.Exists(fileNames[i]))
                                    File.Delete(fileNames[i]);
                            }
                            else if (faceAttributes[0]?.Gender == "female")//Это условия пропускается из-за того, что Gender = null 
                            {
                                File.Move(fileNames[i], endDir + "/Women/" + fileNames[0].Substring(fileNames[0].LastIndexOf('/') + 1));
                                if(File.Exists(fileNames[i]))
                                    File.Delete(fileNames[i]);
                            }
                        }
                    }
                    else
                    {
                        File.Move(fileNames[i], endDir + "/Not a human/" + fileNames[0].Substring(fileNames[0].LastIndexOf('/') + 1));
                        if(File.Exists(fileNames[i]))
                            File.Delete(fileNames[i]);
                    }
                }
                catch(Exception ex)
                {
                    StatusLabel.StringValue = ex.Message;     
                }
                Thread.Sleep(3000);
            }

Image example:

Everything is ok on the site, but the property still returns null.

Answer 1

If the face is not found, what is returned?
(there is an overload where you can specify the necessary attributes)