fix nullable warnings

src/Workspaces/Core/Portable/Editing/ImportAdder.cs

@@ -9,6 +9,7 @@
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Text;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Editing
 {
@@ -52,6 +53,7 @@ public static Task<Document> AddImportsAsync(Document document, IEnumerable<Text
         internal static async Task<Document> AddImportsFromSyntaxesAsync(Document document, bool safe = true, OptionSet? options = null, CancellationToken cancellationToken = default)
         {
             var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            Contract.ThrowIfNull(root);
             return await AddImportsFromSyntaxesAsync(document, root.FullSpan, safe, options, cancellationToken).ConfigureAwait(false);
         }
 
@@ -69,6 +71,7 @@ internal static Task<Document> AddImportsFromSyntaxesAsync(Document document, Te
         internal static async Task<Document> AddImportsFromSyntaxesAsync(Document document, SyntaxAnnotation annotation, bool safe = true, OptionSet? options = null, CancellationToken cancellationToken = default)
         {
             var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            Contract.ThrowIfNull(root);
             return await AddImportsFromSyntaxesAsync(document, root.GetAnnotatedNodesAndTokens(annotation).Select(t => t.FullSpan), safe, options, cancellationToken).ConfigureAwait(false);
         }
 
@@ -94,6 +97,7 @@ internal static Task<Document> AddImportsFromSyntaxesAsync(Document document, IE
         internal static async Task<Document> AddImportsFromSymbolAnnotationAsync(Document document, bool safe = true, OptionSet? options = null, CancellationToken cancellationToken = default)
         {
             var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            Contract.ThrowIfNull(root);
             return await AddImportsFromSymbolAnnotationAsync(document, root.FullSpan, safe, options, cancellationToken).ConfigureAwait(false);
         }
 
@@ -111,6 +115,7 @@ internal static Task<Document> AddImportsFromSymbolAnnotationAsync(Document docu
         internal static async Task<Document> AddImportsFromSymbolAnnotationAsync(Document document, SyntaxAnnotation annotation, bool safe = true, OptionSet? options = null, CancellationToken cancellationToken = default)
         {
             var root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            Contract.ThrowIfNull(root);
             return await AddImportsFromSymbolAnnotationAsync(document, root.GetAnnotatedNodesAndTokens(annotation).Select(t => t.FullSpan), safe, options, cancellationToken).ConfigureAwait(false);
         }
 

src/Workspaces/Core/Portable/Editing/ImportAdderService.cs

@@ -40,6 +40,7 @@ public enum Strategy
             options ??= await document.GetOptionsAsync(cancellationToken).ConfigureAwait(false);
 
             var model = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            Contract.ThrowIfNull(model);
             var root = await model.SyntaxTree.GetRootAsync(cancellationToken).ConfigureAwait(false);
             var addImportsService = document.GetLanguageService<IAddImportsService>();
             var generator = SyntaxGenerator.GetGenerator(document);
@@ -68,14 +69,18 @@ public enum Strategy
                 // This will allow us to find it after we have called MakeSafeToAddNamespaces.
                 var annotation = new SyntaxAnnotation();
                 document = document.WithSyntaxRoot(root.ReplaceNode(context, context.WithAdditionalAnnotations(annotation)));
-                root = await document.GetSyntaxRootAsync().ConfigureAwait(false);
+                root = (await document.GetSyntaxRootAsync().ConfigureAwait(false))!;
+
                 model = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+                Contract.ThrowIfNull(model);
 
                 // Make Safe to add namespaces
                 document = document.WithSyntaxRoot(
                    MakeSafeToAddNamespaces(root, namespaceSymbols, model, document.Project.Solution.Workspace, cancellationToken));
-                root = await document.GetSyntaxRootAsync().ConfigureAwait(false);
+                root = (await document.GetSyntaxRootAsync().ConfigureAwait(false))!;
+
                 model = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+                Contract.ThrowIfNull(model);
 
                 // Find the context. It might be null if we have removed the context in the process of complexifying the tree.
                 context = root.DescendantNodesAndSelf().FirstOrDefault(x => x.HasAnnotation(annotation)) ?? root;