异步日志记录抛出NullReferenceException

我试图使用AsyncTargetingPack异步将一些信息记录到针对.NET 4.0的MVC 4控制器操作中的SQL Server。 我会直接跳到.NET 4.5，但我的应用程序存在于Azure中， 我们仍在等待更新 …

此代码按预期工作（一行写入我的数据库，没有抛出exception）：

public class SystemActionLogger : ISystemActionLogger { private readonly ActionBlock<Tuple> actionBlock; public SystemActionLogger(ISystemActionLogEntryRepository repository) { actionBlock = new ActionBlock<Tuple>( entry => TaskEx.Run(async () => { string data = await JsonConvert.SerializeObjectAsync(entry.Item2); await repository.PersistAsync(new SystemActionLogEntry(entry.Item1, data)); })); } public void Log(SystemAction systemAction, object data) { actionBlock.Post(new Tuple(systemAction, data)); } } 

并且此代码抛出NullReferenceException：

 public class SystemActionLogger : ISystemActionLogger { private readonly ActionBlock<Tuple> actionBlock; public SystemActionLogger(ISystemActionLogEntryRepository repository) { actionBlock = new ActionBlock<Tuple>(async entry => { string data = await JsonConvert.SerializeObjectAsync(entry.Item2); await repository.PersistAsync(new SystemActionLogEntry(entry.Item1, data)); }); } public void Log(SystemAction systemAction, object data) { actionBlock.Post(new Tuple(systemAction, data)); } } 

NullReferenceException：“对象引用未设置为对象的实例。”

 Server stack trace: at System.Web.ThreadContext.AssociateWithCurrentThread(Boolean setImpersonationContext) at System.Web.HttpApplication.OnThreadEnterPrivate(Boolean setImpersonationContext) at System.Web.LegacyAspNetSynchronizationContext.CallCallbackPossiblyUnderLock(SendOrPostCallback callback, Object state) at System.Web.LegacyAspNetSynchronizationContext.CallCallback(SendOrPostCallback callback, Object state) at System.Runtime.CompilerServices.TaskAwaiter.c__DisplayClassa.b__0(Task param0) Exception rethrown at [0]: at System.Runtime.CompilerServices.AsyncMethodBuilderCore.b__1(Object state) at System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx) at System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem() at System.Threading.ThreadPoolWorkQueue.Dispatch() 

我没有对exception的可见性，因为它是所有外部代码。 我不明白为什么第二个代码块失败。 这是我最初写的代码。

我究竟做错了什么？

 public static void Event(string key, string message) { Telemetry.Event(key, message).Wait(100); }