Docs: Add null check for Appbar Search (MudBlazor#10103)

Author: ScarletKuro

src/MudBlazor.Docs/Shared/Appbar.razor.cs

@@ -120,8 +120,13 @@ public bool IsSearchDialogOpen
     [Parameter]
     public bool DisplaySearchBar { get; set; } = true;
 
-    private async void OnSearchResult(ApiLinkServiceEntry entry)
+    private async void OnSearchResult(ApiLinkServiceEntry? entry)
     {
+        if (entry is null)
+        {
+            return;
+        }
+
         NavigationManager.NavigateTo(entry.Link);
         await Task.Delay(1000);
         await _searchAutocomplete.ClearAsync();