feat: avoid adding new item when there is not selection in ListBox.

src/Ursa/Controls/AutoCompleteBox/MultiAutoCompleteBox.cs

@@ -1564,10 +1564,7 @@ public partial class MultiAutoCompleteBox : TemplatedControl, IInnerContentContr
     /// <param name="e">The selection changed event data.</param>
     private void OnAdapterSelectionChanged(object? sender, SelectionChangedEventArgs e)
     {
-        // TODO set selection.
-        // SetCurrentValue(SelectedItemProperty, _adapter!.SelectedItem);
         SelectedItems?.Add(_adapter?.SelectedItem);
-        // UpdateTextValue(null);
     }
 
     //TODO Check UpdateTextCompletion

src/Ursa/Controls/AutoCompleteBox/MultiAutoCompleteSelectionAdapter.cs

@@ -258,6 +258,7 @@ public class MultiAutoCompleteSelectionAdapter : ISelectionAdapter
     /// </summary>
     internal void OnCommit()
     {
+        if (_previewSelectedItem is null) return;
         SelectedItem = _previewSelectedItem;
         SelectionChanged?.Invoke(this,
             new SelectionChangedEventArgs(