More work on nullable references

src/Umbraco.Core/Notifications/IStatefulNotification.cs

@@ -4,6 +4,6 @@ namespace Umbraco.Cms.Core.Notifications
 {
     public interface IStatefulNotification : INotification
     {
-        IDictionary<string, object>? State { get; set; }
+        IDictionary<string, object> State { get; set; }
     }
 }

src/Umbraco.Core/Notifications/StatefulNotification.cs

@@ -12,7 +12,7 @@ namespace Umbraco.Cms.Core.Notifications
         /// This can be used by event subscribers to store state in the notification so they easily deal with custom state data between
         /// a starting ("ing") and an ending ("ed") notification
         /// </summary>
-        public IDictionary<string, object>? State
+        public IDictionary<string, object> State
         {
             get => _state ??= new Dictionary<string, object>();
             set => _state = value;