优化空引用

Melskin/Controls/Cascader.xaml.cs

@@ -85,13 +85,13 @@ public class Cascader : Control
 
     private string GetObjectDisplayText(object? item)
     {
-        if (item == null) return "";
+        if (item == null) return string.Empty;
         if (!string.IsNullOrEmpty(DisplayMemberPath))
         {
             var prop = item.GetType().GetProperty(DisplayMemberPath);
-            return prop?.GetValue(item)?.ToString() ?? "";
+            return prop?.GetValue(item)?.ToString() ?? string.Empty;
         }
-        return item.ToString();
+        return item.ToString()!;
     }
 
     // 创建了完整的、非空的 CascadingPanel
@@ -130,7 +130,7 @@ public class Cascader : Control
     private void OnSelectionChanged(object sender, SelectionChangedEventArgs e)
     {
         if (e.AddedItems.Count == 0) return;
-        var selectedItem = e.AddedItems[0];
+        var selectedItem = e.AddedItems[0]!;
         var currentMenu = sender as ItemsControl;
         var parentPanel = CascadingPanel;
         if (parentPanel == null) return;