即使DataContract不匹配，DataContractJsonSerializer也会顺序序列化

Question

string json = taskOfString.Result;
Byte[] bytes = Encoding.Unicode.GetBytes(json);
MemoryStream memoryStream = new MemoryStream(bytes);
DataContractJsonSerializer serializer = new DataContractJsonSerializer(typeof(T));
var data = serializer.ReadObject(memoryStream) as T;
memoryStream.Close();
if (data != null)
    tcs.TrySetResult(data);
else
tcs.TrySetException(new NullReferenceException("data is null"));

我的目标是在返回的memoryStream是json错误时检测错误。但是，变量数据总是返回非空值....