diff --git a/Storage/Storage/Public/LCUser.cs b/Storage/Storage/Public/LCUser.cs
index c1883b9..ef0957e 100644
--- a/Storage/Storage/Public/LCUser.cs
+++ b/Storage/Storage/Public/LCUser.cs
@@ -550,7 +550,7 @@ namespace LeanCloud.Storage {
         }
 
         async Task LinkWithAuthData(string authType, Dictionary<string, object> data) {
-            Dictionary<string, object> oriAuthData = new Dictionary<string, object>(AuthData);
+            Dictionary<string, object> oriAuthData = new Dictionary<string, object>(AuthData ?? new Dictionary<string, object>());
             AuthData = new Dictionary<string, object> {
                 { authType, data }
             };