Initializing T with a proper NullInstance.

This allows for easier testing where client code will not inject T (which would cause null reference exceptions down the line).

src/Orchard.Web/Modules/Orchard.Users/Activities/UserActivity.cs

@@ -6,6 +6,10 @@ using Orchard.Workflows.Services;
 
 namespace Orchard.Users.Activities {
     public abstract class UserActivity : Event {
+        protected UserActivity() {
+            T = NullLocalizer.Instance;
+        }
+
         public Localizer T { get; set; }
 
         public override bool CanStartWorkflow {