[Combobox] Fix binding to a value not in the list items

When getting the combobox content, the `Value` should be returned instead of `null`. If no `Value` has been set, `null` will still be returned.

Author: vnbaaij

examples/Demo/Shared/Microsoft.FluentUI.AspNetCore.Components.xml

@@ -1794,6 +1794,14 @@
         <member name="P:Microsoft.FluentUI.AspNetCore.Components.SelectColumn`1.SortBy">
             <inheritdoc />
         </member>
+        <member name="P:Microsoft.FluentUI.AspNetCore.Components.SelectColumn`1.Comparer">
+            <summary>
+            Gets or sets the equality comparer used to determine whether two grid items are equal.
+            </summary>
+            <remarks>If not set, the default equality comparer for <typeparamref name="TGridItem"/> is used.
+            Setting this property allows customization of how grid items are compared for equality, which can affect
+            operations such as selection, filtering, or updating items in the grid.</remarks>
+        </member>
         <member name="M:Microsoft.FluentUI.AspNetCore.Components.SelectColumn`1.ClearSelection">
             <summary>
             Allows to clear the selection.

src/Core/Components/List/FluentCombobox.razor.cs

@@ -141,7 +141,7 @@ public override async Task SetParametersAsync(ParameterView parameters)
     protected override async Task ChangeHandlerAsync(ChangeEventArgs e)
     {
 
-        if (e.Value is not null && Items is not null)
+        if (e.Value is not null && Items is not null )
         {
             var value = e.Value.ToString();
             var item = Items.FirstOrDefault(i => GetOptionText(i) == value);
@@ -171,7 +171,7 @@ protected override async Task ChangeHandlerAsync(ChangeEventArgs e)
         }
         else
         {
-            return null;
+            return Value;
         }
     }
 

tests/Core/List/FluentComboboxTests.FluentCombobox_ClearSelection.verified.html

@@ -1,5 +1,5 @@
 
 <style>#myComponent::part(listbox) {  z-index: 9995 }</style>
-<fluent-combobox id="xxx" position="below" blazor:oncomboboxchange="1" blazor:oncontrolinput="2" blazor:elementreference="">
+<fluent-combobox id="xxx" current-value="" position="below" blazor:oncomboboxchange="1" blazor:oncontrolinput="2" blazor:elementreference="">
   <fluent-option id="xxx" value="Contoso" blazor:onclick="3" aria-selected="false" blazor:elementreference="">Contoso</fluent-option>
-</fluent-combobox>
+</fluent-combobox>