[NullReferenceException: 未将对象引用设置到对象的实例。]
   System.Data.SqlClient.SqlConnection.TryOpenInner(TaskCompletionSource`1 retry) +208
   System.Data.SqlClient.SqlConnection.TryOpen(TaskCompletionSource`1 retry) +264
   System.Data.SqlClient.SqlConnection.Open() +132
   System.Data.Entity.Infrastructure.Interception.InternalDispatcher`1.Dispatch(TTarget target, Action`2 operation, TInterceptionContext interceptionContext, Action`3 executing, Action`3 executed) +964
   System.Data.Entity.Infrastructure.Interception.DbConnectionDispatcher.Open(DbConnection connection, DbInterceptionContext interceptionContext) +503
   System.Data.Entity.SqlServer.<>c__DisplayClass1.b__0() +18
   System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func`1 operation) +234
   System.Data.Entity.Core.EntityClient.EntityConnection.Open() +746
   System.Data.Entity.Core.Objects.ObjectContext.EnsureConnection(Boolean shouldMonitorTransactions) +167
   System.Data.Entity.Core.Objects.ObjectContext.ExecuteInTransaction(Func`1 func, IDbExecutionStrategy executionStrategy, Boolean startLocalTransaction, Boolean releaseConnectionOnSuccess) +63
   System.Data.Entity.Core.Objects.<>c__DisplayClass7.b__5() +203
   System.Data.Entity.SqlServer.DefaultSqlExecutionStrategy.Execute(Func`1 operation) +234
   System.Data.Entity.Core.Objects.ObjectQuery`1.GetResults(Nullable`1 forMergeOption) +357
   System.Data.Entity.Core.Objects.ObjectQuery`1..GetEnumerator>b__0() +30
   System.Data.Entity.Internal.LazyEnumerator`1.MoveNext() +39
   System.Linq.Enumerable.FirstOrDefault(IEnumerable`1 source) +209
   PhysicsScience.Common.Repository.EfRepositoryBase`1.Find(Expression`1 exp) +149
   PhysicsScience.Areas.Core.Controllers.HtmlExtensions.TeacherName(Int32 id, String UsersID, String version) +3806
   ASP._Page_Views_Shared__ContentShow_cshtml.Execute() in d:\PhysicsScience\Views\Shared\_ContentShow.cshtml:10
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy() +252
   System.Web.Mvc.WebViewPage.ExecutePageHierarchy() +148
   System.Web.WebPages.WebPageBase.ExecutePageHierarchy(WebPageContext pageContext, TextWriter writer, WebPageRenderingBase startPage) +122
   System.Web.WebPages.<>c__DisplayClass40_0.b__0(TextWriter writer) +309
   System.Web.WebPages.WebPageBase.Write(HelperResult result) +108
   System.Web.WebPages.WebPageBase.RenderSurrounding(String partialViewName, Action`1 body) +89
   System.Web.WebPages.WebPageBase.PopContext() +310
   System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) +378
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +91
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultFilterRecursive(IList`1 filters, Int32 filterIndex, ResultExecutingContext preContext, ControllerContext controllerContext, ActionResult actionResult) +795
   System.Web.Mvc.ControllerActionInvoker.InvokeActionResultWithFilters(ControllerContext controllerContext, IList`1 filters, ActionResult actionResult) +81
   System.Web.Mvc.Async.<>c__DisplayClass3_1.b__5(IAsyncResult asyncResult) +188
   System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) +38
   System.Web.Mvc.<>c.b__152_1(IAsyncResult asyncResult, ExecuteCoreState innerState) +29
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +73
   System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) +52
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +39
   System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) +38
   System.Web.Mvc.<>c.b__20_1(IAsyncResult asyncResult, ProcessRequestState innerState) +43
   System.Web.Mvc.Async.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) +73
   System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) +38
   System.Web.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +431
   System.Web.HttpApplication.ExecuteStepImpl(IExecutionStep step) +75
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +158