Editing Product Variants results in error

I almost finished my front end modification and I see this critical problem at 2.1 and 2.2, its actually a show stopper for me to move forward, any help would be appreciated. Thank U

Edit Product Details  - Product Variants tab - Edit - Click throws Exception


NullReferenceException: Object reference not set to an instance of an object.]
   Nop.Admin.Controllers.ProductVariantController.PrepareProductVariantModel(ProductVariantModel model, ProductVariant variant, Boolean setPredefinedValues) +438
   Nop.Admin.Controllers.ProductVariantController.Edit(Int32 id) +240
   lambda_method(Closure , ControllerBase , Object[] ) +101
   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.<>c__DisplayClass15.<InvokeActionMethodWithFilters>b__12() +56
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodFilter(IActionFilter filter, ActionExecutingContext preContext, Func`1 continuation) +267
   System.Web.Mvc.<>c__DisplayClass17.<InvokeActionMethodWithFilters>b__14() +20
   System.Web.Mvc.ControllerActionInvoker.InvokeActionMethodWithFilters(ControllerContext controllerContext, IList`1 filters, ActionDescriptor actionDescriptor, IDictionary`2 parameters) +190
   System.Web.Mvc.ControllerActionInvoker.InvokeAction(ControllerContext controllerContext, String actionName) +329
   System.Web.Mvc.Controller.ExecuteCore() +115
   System.Web.Mvc.ControllerBase.Execute(RequestContext requestContext) +93
   System.Web.Mvc.ControllerBase.System.Web.Mvc.IController.Execute(RequestContext requestContext) +10
   System.Web.Mvc.<>c__DisplayClassb.<BeginProcessRequest>b__5() +37
   System.Web.Mvc.Async.<>c__DisplayClass1.<MakeVoidDelegate>b__0() +21
   System.Web.Mvc.Async.<>c__DisplayClass8`1.<BeginSynchronous>b__7(IAsyncResult _) +12
   System.Web.Mvc.Async.WrappedAsyncResult`1.End() +55
   System.Web.Mvc.<>c__DisplayClasse.<EndProcessRequest>b__d() +31
   System.Web.Mvc.SecurityUtil.<GetCallInAppTrustThunk>b__0(Action f) +7
   System.Web.Mvc.SecurityUtil.ProcessInApplicationTrust(Action action) +23
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +59
   System.Web.Mvc.MvcHandler.System.Web.IHttpAsyncHandler.EndProcessRequest(IAsyncResult result) +9
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +8963149
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +184

Have you done any changes to the source code?  Can you please debug PrepareProductVariantModel method of ProductVariantController in order to know where exactly the exception is thrown?

I did not change Assemblies except css files on the front end. But in the back end tables - I did modify few things.

1. Removed countries Except India and USA
2. Removed Currencies Except India and USA

I was getting the same error in 2.1 and hoping a fix at 2.2, I upgraded to 2.2 and the error is same.

Can you please debug PrepareProductVariantModel method of ProductVariantController in order to know where exactly the exception is thrown?