Fix MessageBox for null Caption

HandyControl/Controls/Window/MessageBox.cs

@@ -298,7 +298,7 @@ namespace HandyControl.Controls
                 Owner = ownerWindow,
                 WindowStartupLocation = ownerIsNull ? WindowStartupLocation.CenterScreen : WindowStartupLocation.CenterOwner,
                 ShowTitle = true,
-                Title = caption,
+                Title = caption ?? System.Reflection.Assembly.GetExecutingAssembly().GetName().Name,
                 Topmost = ownerIsNull,
                 _messageBoxResult = defaultResult
             };
@@ -388,4 +388,4 @@ namespace HandyControl.Controls
                    || value == MessageBoxResult.Yes;
         }
     }
-}
+}