How to save IBuffer object into JPG file in IsolatedStorage

Question

So I have an IBuffer object and I want to save its content into the phone Isolated Storage as JPG. I've tried the following but it gives me error NullReferenceException.

I suspect the stream was not created properly but how to make it work with IBuffer?

          using (IsolatedStorageFile store = IsolatedStorageFile.GetUserStoreForApplication())
            {
                using (IsolatedStorageFileStream fileStream = store.CreateFile(filePath))
                {
                    MemoryStream stream = new MemoryStream();
                    photo.ImageBuffer.AsStream().CopyTo(stream);
                    BitmapImage bitmap = new BitmapImage();
                    WriteableBitmap wb = new WriteableBitmap(bitmap);

                    //Encode WriteableBitmap object to a JPEG stream.
                    Extensions.SaveJpeg(wb, fileStream, (int)photo.Dimensions.Width, (int)photo.Dimensions.Height, 0, 100);                       
                }
            }

Error message

{System.NullReferenceException: Object reference not set to an instance of an object.
at MS.Internal.XcpImports.CheckHResult(UInt32 hr)
at MS.Internal.XcpImports.WriteableBitmap_CreateFromSource(WriteableBitmap wb, IntPtr ptrMemory, BitmapSource source, Boolean& bHasProtectedContent)
at System.Windows.Media.Imaging.WriteableBitmap..ctor(BitmapSource source)
at LensBlurX.Helpers.ISOHelper.<SaveJPG>d__0.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
at LensBlurX.Pages.PhotoPage.<SaveAsync>d__12.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
 at System.Runtime.CompilerServices.TaskAwaiter.GetResult()
 at LensBlurX.Pages.PhotoPage.<save_Click>d__1e.MoveNext()}