系统.UriFormatException: Invalid URI: URI为空

我使用的是一个URL，当我把它放在chrome，但在我的VS c#代码相同的URL时使用(公共异步静态任务)

using (var client = new HttpClient(handler))  {    
client.BaseAddress = new Uri(url);    ----------> Error

…

Method threw exception: 
System.AggregateException: One or more errors occurred. ---> System.UriFormatException: Invalid URI: The URI is empty.
Result StackTrace:  
at System.Uri.CreateThis(String uri, Boolean dontEscape, UriKind uriKind)
   at System.Uri..ctor(String uriString)

我确信URL没有畸形，所以我无法找出这个错误的原因。谢谢你的帮助。

var url = "http://services.odata.org/Northwind/Northwind.svc/Employees?$filter=minute%28BirthDate%29";
client.BaseAddress = new Uri(url);