diff --git a/extensions/configuration-editing/src/extension.ts b/extensions/configuration-editing/src/extension.ts
index 8643d5f643c3fc012f4144d12d8f654c029e814b..0503c0ba4cd19be5cabcbf42f0a2d9d825b4a94c 100644
--- a/extensions/configuration-editing/src/extension.ts
+++ b/extensions/configuration-editing/src/extension.ts
@@ -44,12 +44,22 @@ function registerKeybindingsCompletions(): vscode.Disposable {
 	});
 }
 
-function updateLaunchJsonDecorations(editor: vscode.TextEditor) {
+function newCompletionItem(text: string, range: vscode.Range) {
+	const item = new vscode.CompletionItem(JSON.stringify(text));
+	item.kind = vscode.CompletionItemKind.Value;
+	item.textEdit = {
+		range,
+		newText: item.label
+	};
+	return item;
+}
+
+function updateLaunchJsonDecorations(editor: vscode.TextEditor | undefined) {
 	if (!editor || path.basename(editor.document.fileName) !== 'launch.json') {
 		return;
 	}
 
-	const ranges = [];
+	const ranges: vscode.Range[] = [];
 	let addPropertyAndValue = false;
 	visit(editor.document.getText(), {
 		onObjectProperty: (property, offset, length) => {
@@ -68,13 +78,3 @@ function updateLaunchJsonDecorations(editor: vscode.TextEditor) {
 	editor.setDecorations(decoration, ranges);
 }
 
-function newCompletionItem(text: string, range: vscode.Range, documentation?: string) {
-	const item = new vscode.CompletionItem(JSON.stringify(text));
-	item.kind = vscode.CompletionItemKind.Value;
-	item.documentation = documentation;
-	item.textEdit = {
-		range,
-		newText: item.label
-	};
-	return item;
-}
diff --git a/extensions/configuration-editing/tsconfig.json b/extensions/configuration-editing/tsconfig.json
index 8cb1633437728038691588a558cc8917c812ade2..4a9fdbed84519f3908ddb35e7b4a5efa966f8e6b 100644
--- a/extensions/configuration-editing/tsconfig.json
+++ b/extensions/configuration-editing/tsconfig.json
@@ -3,9 +3,10 @@
 		"noLib": true,
 		"target": "es5",
 		"module": "commonjs",
-		"outDir": "./out"
+		"outDir": "./out",
+		"strictNullChecks": true
 	},
 	"exclude": [
 		"node_modules"
 	]
-}
\ No newline at end of file
+}
diff --git a/extensions/extension-editing/src/extension.ts b/extensions/extension-editing/src/extension.ts
index a34c549ac12d6bf859e4021f33271862c49aa650..b7a4189554205fed67eb5bbe56a2da1835fbcaf2 100644
--- a/extensions/extension-editing/src/extension.ts
+++ b/extensions/extension-editing/src/extension.ts
@@ -83,7 +83,7 @@ namespace ast {
 			let end = Number.MAX_VALUE;
 
 			for (let name of dottedName.split('.')) {
-				let idx: number;
+				let idx: number = -1;
 				while ((idx = identifiers.indexOf(name, idx + 1)) >= 0) {
 					let myStart = spans[2 * idx];
 					let myEnd = spans[2 * idx + 1];
diff --git a/extensions/vscode-api-tests/src/utils.ts b/extensions/vscode-api-tests/src/utils.ts
index 1cf42b7636e530dfe77761773a49aaeb763036c1..d22baa8d55a5caead61c69dd8bba745672b23492 100644
--- a/extensions/vscode-api-tests/src/utils.ts
+++ b/extensions/vscode-api-tests/src/utils.ts
@@ -62,7 +62,7 @@ export function cleanUp(): Thenable<any> {
 			}
 		});
 
-		vscode.commands.executeCommand('workbench.action.closeAllEditors').then(null, reject);
+		vscode.commands.executeCommand('workbench.action.closeAllEditors').then(undefined, reject);
 
 	}).then(() => {
 		assert.equal(vscode.window.visibleTextEditors.length, 0);
@@ -76,4 +76,4 @@ export function cleanUp(): Thenable<any> {
 
 		// assert.equal(vscode.workspace.textDocuments.length, 0);
 	});
-}
\ No newline at end of file
+}
diff --git a/extensions/vscode-api-tests/src/window.test.ts b/extensions/vscode-api-tests/src/window.test.ts
index b229fae155f61422daab606f1ef9a066fb25a824..065db16dc2671a46564cf797df1abbaa3d493cb6 100644
--- a/extensions/vscode-api-tests/src/window.test.ts
+++ b/extensions/vscode-api-tests/src/window.test.ts
@@ -19,7 +19,7 @@ suite('window namespace tests', () => {
 			return window.showTextDocument(doc).then((editor) => {
 				const active = window.activeTextEditor;
 				assert.ok(active);
-				assert.ok(pathEquals(active.document.uri.fsPath, doc.uri.fsPath));
+				assert.ok(pathEquals(active!.document.uri.fsPath, doc.uri.fsPath));
 			});
 		});
 	});
diff --git a/extensions/vscode-api-tests/src/workspace.test.ts b/extensions/vscode-api-tests/src/workspace.test.ts
index 37c0f9e3f4f2e4d0589c8bda7cdf1d7b8eff93cd..b963ab62af558120649505686fb7227f0c15f4f9 100644
--- a/extensions/vscode-api-tests/src/workspace.test.ts
+++ b/extensions/vscode-api-tests/src/workspace.test.ts
@@ -6,7 +6,7 @@
 'use strict';
 
 import * as assert from 'assert';
-import { workspace, TextDocument, window, Position, Uri, EventEmitter, WorkspaceEdit } from 'vscode';
+import { workspace, TextDocument, window, Position, Uri, EventEmitter, WorkspaceEdit, Disposable } from 'vscode';
 import { createRandomFile, deleteFile, cleanUp, pathEquals } from './utils';
 import { join, basename } from 'path';
 import * as fs from 'fs';
@@ -48,11 +48,13 @@ suite('workspace-namespace', () => {
 
 	test('textDocuments', () => {
 		assert.ok(Array.isArray(workspace.textDocuments));
-		assert.throws(() => workspace.textDocuments = null);
+		assert.throws(() => (<any>workspace).textDocuments = null);
 	});
 
 	test('rootPath', () => {
-		assert.ok(pathEquals(workspace.rootPath, join(__dirname, '../testWorkspace')));
+		if (workspace.rootPath) {
+			assert.ok(pathEquals(workspace.rootPath, join(__dirname, '../testWorkspace')));
+		}
 		assert.throws(() => workspace.rootPath = 'farboo');
 	});
 
@@ -64,23 +66,22 @@ suite('workspace-namespace', () => {
 		});
 	});
 
-	test('openTextDocument, illegal path', done => {
-		workspace.openTextDocument('funkydonky.txt').then(doc => {
-			done(new Error('missing error'));
+	test('openTextDocument, illegal path', () => {
+		return workspace.openTextDocument('funkydonky.txt').then(doc => {
+			throw new Error('missing error');
 		}, err => {
-			done();
+			// good!
 		});
 	});
 
-	test('openTextDocument, untitled is dirty', function (done) {
+	test('openTextDocument, untitled is dirty', function () {
 		if (process.platform === 'win32') {
-			return done(); // TODO@Joh this test fails on windows
+			return; // TODO@Joh this test fails on windows
 		}
 
-		workspace.openTextDocument(Uri.parse('untitled:' + join(workspace.rootPath, './newfile.txt'))).then(doc => {
+		return workspace.openTextDocument(Uri.parse('untitled:' + join(workspace.rootPath, './newfile.txt'))).then(doc => {
 			assert.equal(doc.uri.scheme, 'untitled');
 			assert.ok(doc.isDirty);
-			done();
 		});
 	});
 
@@ -137,7 +138,7 @@ suite('workspace-namespace', () => {
 
 	test('events: onDidOpenTextDocument, onDidChangeTextDocument, onDidSaveTextDocument', () => {
 		return createRandomFile().then(file => {
-			let disposables = [];
+			let disposables: Disposable[] = [];
 
 			let onDidOpenTextDocument = false;
 			disposables.push(workspace.onDidOpenTextDocument(e => {
@@ -370,7 +371,7 @@ suite('workspace-namespace', () => {
 	});
 
 	test('findFiles', () => {
-		return workspace.findFiles('*.js', null).then((res) => {
+		return workspace.findFiles('*.js').then((res) => {
 			assert.equal(res.length, 1);
 			assert.equal(basename(workspace.asRelativePath(res[0])), 'far.js');
 		});
diff --git a/extensions/vscode-api-tests/tsconfig.json b/extensions/vscode-api-tests/tsconfig.json
index 44066990ddcba8d19d3c121b9c1798734e9b5150..e6fc5096aef213addc4a1c2b6b56903b917b5ac2 100644
--- a/extensions/vscode-api-tests/tsconfig.json
+++ b/extensions/vscode-api-tests/tsconfig.json
@@ -4,9 +4,10 @@
 		"target": "ES5",
 		"outDir": "out",
 		"noLib": true,
-		"sourceMap": true
+		"sourceMap": true,
+		"strictNullChecks": true
 	},
 	"exclude": [
 		"node_modules"
 	]
-}
\ No newline at end of file
+}
diff --git a/extensions/vscode-api-tests/typings/mocha.d.ts b/extensions/vscode-api-tests/typings/mocha.d.ts
index f677473dcdd76f32f6bcf36d2754b8d144578c1d..1a66189a454a86d12a2ee618f6858afcf3b0e3a8 100644
--- a/extensions/vscode-api-tests/typings/mocha.d.ts
+++ b/extensions/vscode-api-tests/typings/mocha.d.ts
@@ -6,7 +6,8 @@
 declare function run(): void;
 
 declare function suite(name: string, fn: (err?) => void);
-declare function test(name: string, fn: (done?: (err?) => void) => void);
+declare function test(name: string, fn: () => void);
+declare function test(name: string, fn: (done: (err?) => void) => void);
 declare function suiteSetup(fn: (done?: (err?) => void) => void);
 declare function suiteTeardown(fn: (done?: (err?) => void) => void);
 declare function setup(fn: (done?: (err?) => void) => void);
diff --git a/src/typings/mocha.d.ts b/src/typings/mocha.d.ts
index f677473dcdd76f32f6bcf36d2754b8d144578c1d..1a66189a454a86d12a2ee618f6858afcf3b0e3a8 100644
--- a/src/typings/mocha.d.ts
+++ b/src/typings/mocha.d.ts
@@ -6,7 +6,8 @@
 declare function run(): void;
 
 declare function suite(name: string, fn: (err?) => void);
-declare function test(name: string, fn: (done?: (err?) => void) => void);
+declare function test(name: string, fn: () => void);
+declare function test(name: string, fn: (done: (err?) => void) => void);
 declare function suiteSetup(fn: (done?: (err?) => void) => void);
 declare function suiteTeardown(fn: (done?: (err?) => void) => void);
 declare function setup(fn: (done?: (err?) => void) => void);