async completion: fixing 'Nullable object must have a value' when deleting the whole word (#32143)

src/EditorFeatures/Core/Implementation/IntelliSense/AsyncCompletion/ItemManager.cs

@@ -329,8 +329,8 @@ private static bool IsAfterDot(ITextSnapshot snapshot, ITrackingSpan applicableT
             return new FilteredCompletionModel(
                 highlightedList, index, filters,
                 hardSelect ? UpdateSelectionHint.Selected : UpdateSelectionHint.SoftSelected,
-                centerSelection: true, 
-                uniqueItem: matchCount == 1 ? bestFilterResult.Value.VSCompletionItem : default);
+                centerSelection: true,
+                uniqueItem: matchCount == 1 ? bestFilterResult.GetValueOrDefault().VSCompletionItem : default);
         }
 
         private FilteredCompletionModel HandleAllItemsFilteredOut(

src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb

@@ -61,6 +61,40 @@ Namespace Microsoft.CodeAnalysis.Editor.UnitTests.IntelliSense
             End Using
         End Function
 
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestDeletingWholeWordResetCompletionToTheDefaultItem(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(completionImplementation,
+                              <Document>
+                                  using System;
+
+class C
+{
+    void M()
+    {
+        var replyUri = new Uri("");
+        $$
+    }
+}
+
+                              </Document>)
+
+                state.Workspace.Options = state.Workspace.Options.WithChangedOption(
+                    CompletionOptions.TriggerOnDeletion, LanguageNames.CSharp, True)
+
+                state.SendTypeChars("repl")
+                state.SendTab()
+                For i = 1 To 7
+                    state.SendBackspace()
+                    Await state.WaitForAsynchronousOperationsAsync()
+                Next
+                Await state.AssertCompletionSession()
+
+                state.SendBackspace()
+                Await state.AssertSelectedCompletionItem("AccessViolationException")
+            End Using
+        End Function
+
         <MemberData(NameOf(AllCompletionImplementations))>
         <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
         Public Async Function TestNotAtStartOfExistingWord(completionImplementation As CompletionImplementation) As Task