diff --git a/src/tsconfig.strictNullChecks.json b/src/tsconfig.strictNullChecks.json
index f0c3958065f..b8c84e0ec3e 100644
--- a/src/tsconfig.strictNullChecks.json
+++ b/src/tsconfig.strictNullChecks.json
@@ -7,11 +7,26 @@
 	"include": [
 		"./typings",
 		"./vs/base/common/charCode.ts",
+		"./vs/base/common/color.ts",
+		"./vs/base/common/comparers.ts",
+		"./vs/base/common/date.ts",
+		"./vs/base/common/decorators.ts",
+		"./vs/base/common/functional.ts",
+		"./vs/base/common/idGenerator.ts",
 		"./vs/base/common/iterator.ts",
-		"./vs/base/common/strings.ts",
+		"./vs/base/common/lifecycle.ts",
+		"./vs/base/common/network.ts",
+		"./vs/base/common/numbers.ts",
+		"./vs/base/common/objects.ts",
 		"./vs/base/common/paths.ts",
 		"./vs/base/common/platform.ts",
+		"./vs/base/common/range.ts",
+		"./vs/base/common/resources.ts",
+		"./vs/base/common/scanCode.ts",
+		"./vs/base/common/severity.ts",
+		"./vs/base/common/strings.ts",
 		"./vs/base/common/uri.ts",
+		"./vs/base/common/urilpc.ts",
 		"./vs/base/common/uuid.ts"
 	],
 	"exclude": [
diff --git a/src/vs/base/common/color.ts b/src/vs/base/common/color.ts
index 6dc7eb65aef..a8df525c7cb 100644
--- a/src/vs/base/common/color.ts
+++ b/src/vs/base/common/color.ts
@@ -416,7 +416,7 @@ export class Color {
 	}
 
 	toString(): string {
-		return Color.Format.CSS.format(this);
+		return '' + Color.Format.CSS.format(this);
 	}
 
 	static getLighterColor(of: Color, relative: Color, factor?: number): Color {
diff --git a/src/vs/base/common/comparers.ts b/src/vs/base/common/comparers.ts
index a1cf984e5ef..a3f3ca3582f 100644
--- a/src/vs/base/common/comparers.ts
+++ b/src/vs/base/common/comparers.ts
@@ -98,7 +98,7 @@ function noIntlCompareFileExtensions(one: string, other: string): number {
 }
 
 function extractNameAndExtension(str?: string): [string, string] {
-	const match = str ? FileNameMatch.exec(str) : [] as RegExpExecArray;
+	const match = str ? FileNameMatch.exec(str) as Array<string> : ([] as Array<string>);
 
 	return [(match && match[1]) || '', (match && match[3]) || ''];
 }
diff --git a/src/vs/base/common/decorators.ts b/src/vs/base/common/decorators.ts
index ad829d14ff6..01478d3c3ad 100644
--- a/src/vs/base/common/decorators.ts
+++ b/src/vs/base/common/decorators.ts
@@ -5,8 +5,8 @@
 
 export function createDecorator(mapFn: (fn: Function, key: string) => Function): Function {
 	return (target: any, key: string, descriptor: any) => {
-		let fnKey: string = null;
-		let fn: Function = null;
+		let fnKey: string | null = null;
+		let fn: Function | null = null;
 
 		if (typeof descriptor.value === 'function') {
 			fnKey = 'value';
@@ -20,19 +20,19 @@ export function createDecorator(mapFn: (fn: Function, key: string) => Function):
 			throw new Error('not supported');
 		}
 
-		descriptor[fnKey] = mapFn(fn, key);
+		descriptor[fnKey!] = mapFn(fn, key);
 	};
 }
 
 export function memoize(target: any, key: string, descriptor: any) {
-	let fnKey: string = null;
-	let fn: Function = null;
+	let fnKey: string | null = null;
+	let fn: Function | null = null;
 
 	if (typeof descriptor.value === 'function') {
 		fnKey = 'value';
 		fn = descriptor.value;
 
-		if (fn.length !== 0) {
+		if (fn!.length !== 0) {
 			console.warn('Memoize should only be used in functions with zero parameters');
 		}
 	} else if (typeof descriptor.get === 'function') {
@@ -46,13 +46,13 @@ export function memoize(target: any, key: string, descriptor: any) {
 
 	const memoizeKey = `$memoize$${key}`;
 
-	descriptor[fnKey] = function (...args: any[]) {
+	descriptor[fnKey!] = function (...args: any[]) {
 		if (!this.hasOwnProperty(memoizeKey)) {
 			Object.defineProperty(this, memoizeKey, {
 				configurable: false,
 				enumerable: false,
 				writable: false,
-				value: fn.apply(this, args)
+				value: fn!.apply(this, args)
 			});
 		}
 
diff --git a/src/vs/base/common/keyCodes.ts b/src/vs/base/common/keyCodes.ts
index 097578a6697..74352496c07 100644
--- a/src/vs/base/common/keyCodes.ts
+++ b/src/vs/base/common/keyCodes.ts
@@ -410,7 +410,7 @@ export function KeyChord(firstPart: number, secondPart: number): number {
 	return (firstPart | chordPart) >>> 0;
 }
 
-export function createKeybinding(keybinding: number, OS: OperatingSystem): Keybinding {
+export function createKeybinding(keybinding: number, OS: OperatingSystem): Keybinding | null {
 	if (keybinding === 0) {
 		return null;
 	}
diff --git a/src/vs/base/common/lifecycle.ts b/src/vs/base/common/lifecycle.ts
index 8b44cd2c687..405752fdb57 100644
--- a/src/vs/base/common/lifecycle.ts
+++ b/src/vs/base/common/lifecycle.ts
@@ -17,7 +17,7 @@ export function isDisposable<E extends object>(thing: E): thing is E & IDisposab
 export function dispose<T extends IDisposable>(disposable: T): T;
 export function dispose<T extends IDisposable>(...disposables: T[]): T[];
 export function dispose<T extends IDisposable>(disposables: T[]): T[];
-export function dispose<T extends IDisposable>(first: T | T[], ...rest: T[]): T | T[] {
+export function dispose<T extends IDisposable>(first: T | T[], ...rest: T[]): T | T[] | undefined {
 	if (Array.isArray(first)) {
 		first.forEach(d => d && d.dispose());
 		return [];
diff --git a/src/vs/base/common/objects.ts b/src/vs/base/common/objects.ts
index 2cc8e033d2b..5e90f440f07 100644
--- a/src/vs/base/common/objects.ts
+++ b/src/vs/base/common/objects.ts
@@ -218,7 +218,7 @@ export function safeStringify(obj: any): string {
 	});
 }
 
-export function getOrDefault<T, R>(obj: T, fn: (obj: T) => R, defaultValue: R = null): R {
+export function getOrDefault<T, R>(obj: T, fn: (obj: T) => R, defaultValue: R | null = null): R | null {
 	const result = fn(obj);
 	return typeof result === 'undefined' ? defaultValue : result;
 }
diff --git a/src/vs/base/common/resources.ts b/src/vs/base/common/resources.ts
index 811d2f38d79..7df851fa3db 100644
--- a/src/vs/base/common/resources.ts
+++ b/src/vs/base/common/resources.ts
@@ -72,7 +72,7 @@ export function basename(resource: URI): string {
  * @param resource The input URI.
  * @returns The URI representing the directory of the input URI.
  */
-export function dirname(resource: URI): URI {
+export function dirname(resource: URI): URI | null {
 	let dirname = paths.dirname(resource.path, '/');
 	if (resource.authority && dirname.length && dirname.charCodeAt(0) !== CharCode.Slash) {
 		return null; // If a URI contains an authority component, then the path component must either be empty or begin with a CharCode.Slash ("/") character