UrlHelper.GetParam(url, "a");
未将对象引用设置到对象的实例。
  说明: 执行当前 Web 请求期间，出现未经处理的异常。请检查堆栈跟踪信息，以了解有关该错误以及代码中导致错误的出处的详细信息。

 异常详细信息: System.NullReferenceException: 未将对象引用设置到对象的实例。

源错误:

执行当前 Web 请求期间生成了未经处理的异常。可以使用下面的异常堆栈跟踪信息确定有关异常原因和发生位置的信息。

堆栈跟踪:

[NullReferenceException: 未将对象引用设置到对象的实例。]
   Dev.Framework.FileServer.ImageFile.ImageUploader.Thumbnail(Stream stream, Int32 maxwith, Int32 maxheight, String watermark) in c:\Users\Administrator\Source\Repos\Dev.All\DevLibs\Framework\FileServer\Dev.Framework.FileServer.Impl\ImageFile\ImageUploader.cs:268
   Dev.Framework.FileServer.ImageFile.ImageUploader.Watermark(Stream stream, String watermark) in c:\Users\Administrator\Source\Repos\Dev.All\DevLibs\Framework\FileServer\Dev.Framework.FileServer.Impl\ImageFile\ImageUploader.cs:135
   GameGroup.Group.Web.Controllers.BBSController.UploadJson() in c:\Code\游戏团\GameGroup\Presentation\GameGroup.Group.Web\Controllers\BBSController.cs:928
   lambda_method(Closure , ControllerBase , Object[] ) +62
   System.Web.Mvc.ActionMethodDispatcher.Execute(ControllerBase controller, Object[] parameters) +17
   System.Web.Mvc.ReflectedActionDescriptor.Execute(ControllerContext controllerContext, IDictionary`2 parameters) +188
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +27
   System.Web.Mvc.Async.<>c__DisplayClass42.<BeginInvokeSynchronousActionMethod>b__41() +28
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +50
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) +29
   System.Web.Mvc.Async.<>c__DisplayClass39.<BeginInvokeActionMethodWithFilters>b__33() +59
   System.Web.Mvc.Async.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49() +240
   System.Web.Mvc.Async.<>c__DisplayClass4f.<InvokeActionMethodFilterAsynchronously>b__49() +240
   System.Web.Mvc.Async.<>c__DisplayClass37.<BeginInvokeActionMethodWithFilters>b__36(IAsyncResult asyncResult) +12
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +50
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) +31
   System.Web.Mvc.Async.<>c__DisplayClass2a.<BeginInvokeAction>b__20() +23
   System.Web.Mvc.Async.<>c__DisplayClass25.<BeginInvokeAction>b__22(IAsyncResult asyncResult) +128
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +50