ArgumentNullException: 值不能为 null。
参数名: fontFamily
StackTrace:
   在 System.Windows.Media.Typeface..ctor(FontFamily fontFamily, FontStyle style, FontWeight weight, FontStretch stretch, FontFamily fallbackFontFamily)
   在 VerifyCodeHelper.DrawingContextHelper.GetFormattedText(String text, Brush color, FlowDirection flowDirection, Double textSize, FontWeight fontWeight)
   在 VerifyCodeHelper.VerifyCode.CreateCheckCodeImage(String checkCode, Int32 width, Int32 height)
   在 VerifyCodeHelper.VerifyCode.CheckCode_Loaded(Object sender, RoutedEventArgs e)
   在 System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
   在 System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
   在 System.Windows.BroadcastEventHelper.BroadcastEvent(DependencyObject root, RoutedEvent routedEvent)
   在 System.Windows.BroadcastEventHelper.BroadcastLoadedEvent(Object root)
   在 MS.Internal.LoadedOrUnloadedOperation.DoWork()
   在 System.Windows.Media.MediaContext.FireLoadedPendingCallbacks()
   在 System.Windows.Media.MediaContext.FireInvokeOnRenderCallbacks()
   在 System.Windows.Media.MediaContext.RenderMessageHandlerCore(Object resizedCompositionTarget)
   在 System.Windows.Media.MediaContext.RenderMessageHandler(Object resizedCompositionTarget)
   在 System.Windows.Interop.HwndTarget.OnResize()
   在 System.Windows.Interop.HwndTarget.HandleMessage(WindowMessage msg, IntPtr wparam, IntPtr lparam)
   在 System.Windows.Interop.HwndSource.HwndTargetFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   在 MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
   在 MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
   在 System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
   在 System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)