asp.net-mvc-4 - 在 MVC 4 应用程序中使用带有异步/等待的 HttpClient 的空引用异常

Question

我正在使用 HttpClient 调用 REST API。如果我从测试项目中调用 HttpClient.GetAsync 方法，它可以正常工作。但是从 MVC 4 应用程序调用 HttpClient.GetAsync() 会引发未处理的对象引用未设置异常，并具有以下堆栈跟踪：

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.Web.LegacyAspNetSynchronizationContext.Post(SendOrPostCallback callback, Object state) 
at System.Threading.Tasks.SynchronizationContextAwaitTaskContinuation.PostAction(Object state) 
at System.Threading.Tasks.AwaitTaskContinuation.RunCallback(ContextCallback callback, Object state, Task& currentTask) 
--- End of stack trace from previous location where exception was thrown --- 
at System.Threading.Tasks.AwaitTaskContinuation.<ThrowAsyncIfNecessary>b__1(Object s) 
at System.Threading.QueueUserWorkItemCallback.WaitCallback_Context(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() 
at System.Threading._ThreadPoolWaitCallback.PerformWaitCallback()

我正在运行 .NET Framework 4.5。任何想法如何解决它。