diff --git a/extensions/typescript-language-features/src/features/task.ts b/extensions/typescript-language-features/src/features/task.ts
index 6d6f1e04f46e5a6cbab905304e9e6dcae7724420..c71f3c4435daa14925d10bfb651a5395ef4c32c0 100644
--- a/extensions/typescript-language-features/src/features/task.ts
+++ b/extensions/typescript-language-features/src/features/task.ts
@@ -158,7 +158,7 @@ class TscTaskProvider implements vscode.TaskProvider {
 		return undefined;
 	}
 
-	private getActiveTypeScriptFile(): string | null {
+	private getActiveTypeScriptFile(): string | undefined {
 		const editor = vscode.window.activeTextEditor;
 		if (editor) {
 			const document = editor.document;
@@ -166,7 +166,7 @@ class TscTaskProvider implements vscode.TaskProvider {
 				return this.client.value.toPath(document.uri);
 			}
 		}
-		return null;
+		return undefined;
 	}
 
 	private async getTasksForProject(project: TSConfig): Promise<vscode.Task[]> {
diff --git a/extensions/typescript-language-features/src/typescriptService.ts b/extensions/typescript-language-features/src/typescriptService.ts
index 802a8c475eb692af10430fa61f204ea3558d8699..a81024f0063760f2ce8f99fc9674ceaafe950bc1 100644
--- a/extensions/typescript-language-features/src/typescriptService.ts
+++ b/extensions/typescript-language-features/src/typescriptService.ts
@@ -63,14 +63,14 @@ export interface ITypeScriptServiceClient {
 	 *
 	 * Does not try handling case insensitivity.
 	 */
-	normalizedPath(resource: vscode.Uri): string | null;
+	normalizedPath(resource: vscode.Uri): string | undefined;
 
 	/**
 	 * Map a resource to a normalized path
 	 *
 	 * This will attempt to handle case insensitivity.
 	 */
-	toPath(resource: vscode.Uri): string | null;
+	toPath(resource: vscode.Uri): string | undefined;
 
 	/**
 	 * Convert a path to a resource.
diff --git a/extensions/typescript-language-features/src/typescriptServiceClient.ts b/extensions/typescript-language-features/src/typescriptServiceClient.ts
index 6298b5fb4b7e418d36f42d7cf5a0bcab2846c8be..cac72950ecf0251e57d371954ae768d2f8f09ec9 100644
--- a/extensions/typescript-language-features/src/typescriptServiceClient.ts
+++ b/extensions/typescript-language-features/src/typescriptServiceClient.ts
@@ -488,7 +488,7 @@ export default class TypeScriptServiceClient extends Disposable implements IType
 		}
 	}
 
-	public normalizedPath(resource: vscode.Uri): string | null {
+	public normalizedPath(resource: vscode.Uri): string | undefined {
 		if (this._apiVersion.gte(API.v213)) {
 			if (resource.scheme === fileSchemes.walkThroughSnippet || resource.scheme === fileSchemes.untitled) {
 				const dirName = path.dirname(resource.path);
@@ -498,19 +498,19 @@ export default class TypeScriptServiceClient extends Disposable implements IType
 		}
 
 		if (resource.scheme !== fileSchemes.file) {
-			return null;
+			return undefined;
 		}
 
 		const result = resource.fsPath;
 		if (!result) {
-			return null;
+			return undefined;
 		}
 
 		// Both \ and / must be escaped in regular expressions
 		return result.replace(new RegExp('\\' + this.pathSeparator, 'g'), '/');
 	}
 
-	public toPath(resource: vscode.Uri): string | null {
+	public toPath(resource: vscode.Uri): string | undefined {
 		return this.normalizedPath(resource);
 	}
 
diff --git a/extensions/typescript-language-features/src/utils/managedFileContext.ts b/extensions/typescript-language-features/src/utils/managedFileContext.ts
index f88e90e19e087640ffc2cc498f41ee50c3df39bd..36cca539ec3042f18ef3619ff520ad2b749a4f38 100644
--- a/extensions/typescript-language-features/src/utils/managedFileContext.ts
+++ b/extensions/typescript-language-features/src/utils/managedFileContext.ts
@@ -17,7 +17,7 @@ export default class ManagedFileContextManager {
 	private readonly onDidChangeActiveTextEditorSub: vscode.Disposable;
 
 	public constructor(
-		private readonly normalizePath: (resource: vscode.Uri) => string | null
+		private readonly normalizePath: (resource: vscode.Uri) => string | undefined
 	) {
 		this.onDidChangeActiveTextEditorSub = vscode.window.onDidChangeActiveTextEditor(this.onDidChangeActiveTextEditor, this);
 
diff --git a/extensions/typescript-language-features/src/utils/resourceMap.ts b/extensions/typescript-language-features/src/utils/resourceMap.ts
index 33d6f00b4be8af2d4bdebcee4959eba3b7af9df4..a10fbd91636a274d57c75b5078a45dfd5ee190f8 100644
--- a/extensions/typescript-language-features/src/utils/resourceMap.ts
+++ b/extensions/typescript-language-features/src/utils/resourceMap.ts
@@ -18,7 +18,7 @@ export class ResourceMap<T> {
 	private readonly _map = new Map<string, { resource: vscode.Uri, value: T }>();
 
 	constructor(
-		private readonly _normalizePath: (resource: vscode.Uri) => string | null = (resource) => resource.fsPath
+		private readonly _normalizePath: (resource: vscode.Uri) => string | undefined = (resource) => resource.fsPath
 	) { }
 
 	public get size() {
@@ -71,7 +71,7 @@ export class ResourceMap<T> {
 		return this._map.values();
 	}
 
-	private toKey(resource: vscode.Uri): string | null {
+	private toKey(resource: vscode.Uri): string | undefined {
 		const key = this._normalizePath(resource);
 		if (!key) {
 			return key;
diff --git a/extensions/typescript-language-features/src/utils/versionStatus.ts b/extensions/typescript-language-features/src/utils/versionStatus.ts
index 2b6901ee3d15e56e20b9293038d295c6c85092ea..6d7940c9a8a273128bad0155daee676a7236d82d 100644
--- a/extensions/typescript-language-features/src/utils/versionStatus.ts
+++ b/extensions/typescript-language-features/src/utils/versionStatus.ts
@@ -12,7 +12,7 @@ export default class VersionStatus {
 	private readonly _versionBarEntry: vscode.StatusBarItem;
 
 	constructor(
-		private readonly _normalizePath: (resource: vscode.Uri) => string | null
+		private readonly _normalizePath: (resource: vscode.Uri) => string | undefined
 	) {
 		this._versionBarEntry = vscode.window.createStatusBarItem(vscode.StatusBarAlignment.Right, 99 /* to the right of editor status (100) */);
 		this._onChangeEditorSub = vscode.window.onDidChangeActiveTextEditor(this.showHideStatus, this);