Fix merge issues that made filtering completion to nothing crash VS

Fixes #11559

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Controller.cs

@@ -125,8 +125,8 @@ internal override void OnModelUpdated(Model modelOpt)
             else
             {
                 var selectedItem = modelOpt.SelectedItem;
-                var viewSpan = modelOpt.GetViewBufferSpan(selectedItem.Item.Span);
-                var triggerSpan = modelOpt.GetCurrentSpanInSnapshot(viewSpan, this.TextView.TextSnapshot)
+                var viewSpan = selectedItem == null ? (ViewTextSpan?)null : modelOpt.GetViewBufferSpan(selectedItem.Item.Span);
+                var triggerSpan = viewSpan == null ? null : modelOpt.GetCurrentSpanInSnapshot(viewSpan.Value, this.TextView.TextSnapshot)
                                           .CreateTrackingSpan(SpanTrackingMode.EdgeInclusive);
 
                 sessionOpt.PresenterSession.PresentItems(

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Model.cs

@@ -62,10 +62,7 @@ internal class Model
             ITrackingPoint commitSpanEndPoint,
             bool dismissIfEmpty)
         {
-            Contract.ThrowIfNull(selectedItem);
             Contract.ThrowIfFalse(totalItems.Length != 0, "Must have at least one item.");
-            Contract.ThrowIfFalse(filteredItems.Length != 0, "Must have at least one filtered item.");
-            Contract.ThrowIfFalse(filteredItems.Contains(selectedItem) || defaultSuggestionModeItem == selectedItem, "Selected item must be in filtered items.");
 
             _disconnectedBufferGraph = disconnectedBufferGraph;
             this.OriginalList = originalList;

src/EditorFeatures/Core/Implementation/IntelliSense/Completion/Presentation/RoslynCompletionSet.cs

@@ -87,12 +87,16 @@ void ICompletionSet.SetTrackingSpan(ITrackingSpan trackingSpan)
 
                 var applicableToText = this.ApplicableTo.GetText(this.ApplicableTo.TextBuffer.CurrentSnapshot);
 
-                var filteredSuggestionModeItem = new SimplePresentationItem(
+                SimplePresentationItem filteredSuggestionModeItem = null;
+                if (selectedItem != null)
+                {
+                    filteredSuggestionModeItem = new SimplePresentationItem(
                         CompletionItem.Create(
                             displayText: applicableToText,
                             span: this.ApplicableTo.GetSpan(this.ApplicableTo.TextBuffer.CurrentSnapshot).Span.ToTextSpan()),
                         selectedItem.CompletionService,
                         isSuggestionModeItem: true);
+                }
 
                 var showBuilder = suggestionMode || presetBuilder != null;
                 var bestSuggestionModeItem = applicableToText.Length > 0 ? filteredSuggestionModeItem : presetBuilder ?? filteredSuggestionModeItem;