fix: 修复数据源为 null 时赋值逻辑

Author: ArgoZhang

src/BootstrapBlazor/Components/Cascader/Cascader.razor.cs

@@ -133,10 +133,16 @@ protected override void OnParametersSet()
         SubMenuIcon ??= IconTheme.GetIconByKey(ComponentIcons.CascaderSubMenuIcon);
         ClearIcon ??= IconTheme.GetIconByKey(ComponentIcons.SelectClearIcon);
 
-        Items ??= [];
-
         PlaceHolder ??= Localizer[nameof(PlaceHolder)];
 
+        Items ??= [];
+        if (!Items.Any())
+        {
+            _lastValue = string.Empty;
+            Value = default;
+            return;
+        }
+
         if (_lastValue != CurrentValueAsString)
         {
             _lastValue = CurrentValueAsString;