fix null reference exception (#32)

Author: ElderJames

src/layout/src/BasicLayout.razor.cs

@@ -31,7 +31,7 @@ public partial class BasicLayout : IBasicLayout
         [Parameter] public MenuDataItem[] MenuData { get; set; }
         [Parameter] public MenuMode Mode { get; set; }
         [Parameter] public EventCallback<bool> OnCollapse { get; set; }
-        [Parameter] public string[] OpenKeys { get; set; }
+        [Parameter] public string[] OpenKeys { get; set; } = { };
         [Parameter] public MenuTheme Theme { get; set; }
         [Parameter] public OneOf<string, RenderFragment> Logo { get; set; }
         [Parameter] public int SiderWidth { get; set; } = 208;

src/layout/src/SiderMenu/SiderMenu.razor.cs

@@ -34,7 +34,7 @@ public partial class SiderMenu : ISiderMenu
         [Parameter] public MenuDataItem[] MenuData { get; set; }
         [Parameter] public MenuMode Mode { get; set; } = MenuMode.Inline;
         [Parameter] public EventCallback<bool> OnCollapse { get; set; }
-        [Parameter] public string[] OpenKeys { get; set; }
+        [Parameter] public string[] OpenKeys { get; set; } = { };
         [Parameter] public OneOf<string, RenderFragment> Logo { get; set; }
         [Parameter] public int SiderWidth { get; set; } = 208;
         [Parameter] public BreakpointType Breakpoint { get; set; } = BreakpointType.Lg;