Item Drop Bug

When I drop an item, it gives me this error message.

"Object reference not set to an instance of an object."

Here's the Stack trace.

at TT.Web.Controllers.PvPController.Drop(Int32 itemId) in C:\Games\tt-game\src\TT.Web\Controllers\PvPController.cs:line 2156 at lambda_method(Closure , ControllerBase , Object[] ) at System.Web.Mvc.ControllerActionInvoker.InvokeActionMethod(ControllerContext controllerContext, ActionDescriptor actionDescriptor, IDictionary2 parameters) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c.<BeginInvokeSynchronousActionMethod>b__9_0(IAsyncResult asyncResult, ActionInvocation innerInvokeState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult2.CallEndDelegate(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethod(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_0.b__0() at System.Web.Mvc.Async.AsyncControllerActionInvoker.AsyncInvocationWithFilters.<>c__DisplayClass11_2.b__2() at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeActionMethodWithFilters(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass3_5.b__4() at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass3_0.b__1(IAsyncResult asyncResult)