InvalidOperationException: 提供的请求 URI 无效。请求 URI 必须为绝对 URI 或必须设置 BaseAddress。
StackTrace:
   在 System.Net.Http.HttpClient.PrepareRequestMessage(HttpRequestMessage request)
   在 System.Net.Http.HttpClient.SendAsync(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationToken cancellationToken)
   在 System.Net.Http.HttpClient.GetAsync(Uri requestUri, HttpCompletionOption completionOption, CancellationToken cancellationToken)
   在 DynamicClass.<Exec>d__0.MoveNext()
--- 引发异常的上一位置中堆栈跟踪的末尾 ---
   在 System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
   在 System.Threading.ExecutionContext.RunInternal(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   在 System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean preserveSyncCtx)
   在 System.Threading.QueueUserWorkItemCallback.System.Threading.IThreadPoolWorkItem.ExecuteWorkItem()
   在 System.Threading.ThreadPoolWorkQueue.Dispatch()