在VB.Net WebMethod中反序列化JSON不起作用

我在调用WebMethod时试图反序列化JSON对象。反序列化成功地创建了对象数组,但值为“Nothing”。我做错什么了?

public class Data
{
    public Attribute[] Attributes{ get; set; }
}

public class Attribute
{
    public string Category { get; set; }
    public string Value { get; set; }

}

这是我的网络方法:

<System.Web.Services.WebMethod()>
Public Shared Function A_Method(ByVal Attributes As Data)
    'do things
End Function

下面是传递给WebMethod的JSON对象:

{"Attributes":[
   {
      "Attribute":{
         "Category":"Category1",
         "Value":"Value1"
      }
   },
   {
      "Attribute":{
         "Category":"Category2",
         "Value":"Value2"
      }
   },
   {
      "Attribute":{
         "Category":"Category3",
         "Value":"Value3"
      }
   },
   {
      "Attribute":{
         "Category":"Category4",
         "Value":"Value4"
      }
   },
   {
      "Attribute":{
         "Category":"Category5",
         "Value":"Value5"
      }
   },
   {
      "Attribute":{
         "Category":"Category6",
         "Value":"Value6"
      }
   },
   {
      "Attribute":{
         "Category":"Category7",
         "Value":"Value7"
      }
   }
]
}