[MessageBar] Fix NullReferenceException and thread safety in MessageService

src/Core/Components/DataGrid/FluentDataGrid.razor.cs

@@ -372,7 +372,7 @@ public partial class FluentDataGrid<TGridItem> : FluentComponentBase, IHandleEve
 
     // Returns Loading if set (controlled). If not controlled,
     // we assume the grid is loading until the next data load completes
-    internal bool EffectiveLoadingValue => Loading ?? ItemsProvider is not null;
+    internal bool EffectiveLoadingValue => Loading ?? (ItemsProvider is not null);
 
     private ElementReference? _gridReference;
     //private DotNetObjectReference<Type>? _dotNetObjectReference;

src/Core/Components/MessageBar/Services/MessageService.cs

@@ -46,7 +46,7 @@
             MessageLock.EnterReadLock();
             try
             {
-                return MessageList;
+                return MessageList.ToList();
             }
             finally
             {
@@ -66,11 +66,19 @@
         MessageLock.EnterReadLock();
         try
         {
-            var messages = string.IsNullOrEmpty(section)
-                       ? MessageList
-                       : MessageList.Where(x => x.Section == section);
+            IEnumerable<Message> messages = MessageList;
 
-            return count > 0 ? messages.Take(count) : messages;
+            if (!string.IsNullOrEmpty(section))
+            {
+                messages = messages.Where(x => x.Section == section);
+            }
+
+            if (count > 0)
+            {
+                messages = messages.Take(count);
+            }
+
+            return messages.ToList();
         }
         finally
         {
@@ -263,7 +271,10 @@
             MessageLock.ExitWriteLock();
         }
 
-        await OnMessageItemsUpdatedAsync!.Invoke();
+        if (OnMessageItemsUpdatedAsync is { } handler)
+        {
+            await handler.Invoke();
+        }
 
         return message;
     }
@@ -326,7 +337,7 @@
     /// <summary />
     public void Dispose()
     {
         if (_navigationManager != null)
         {
             _navigationManager.LocationChanged -= NavigationManager_LocationChanged;
         }