diff --git a/src/vs/base/browser/touch.ts b/src/vs/base/browser/touch.ts
index db93de17f5812..c85416054f010 100644
--- a/src/vs/base/browser/touch.ts
+++ b/src/vs/base/browser/touch.ts
@@ -192,28 +192,28 @@ export class Gesture extends Disposable {
 				holdTime = Date.now() - data.initialTimeStamp;
 
 			if (holdTime < Gesture.HOLD_DELAY
-				&& Math.abs(data.initialPageX - arrays.tail(data.rollingPageX)) < 30
-				&& Math.abs(data.initialPageY - arrays.tail(data.rollingPageY)) < 30) {
+				&& Math.abs(data.initialPageX - arrays.tail(data.rollingPageX)!) < 30
+				&& Math.abs(data.initialPageY - arrays.tail(data.rollingPageY)!) < 30) {
 
 				const evt = this.newGestureEvent(EventType.Tap, data.initialTarget);
-				evt.pageX = arrays.tail(data.rollingPageX);
-				evt.pageY = arrays.tail(data.rollingPageY);
+				evt.pageX = arrays.tail(data.rollingPageX)!;
+				evt.pageY = arrays.tail(data.rollingPageY)!;
 				this.dispatchEvent(evt);
 
 			} else if (holdTime >= Gesture.HOLD_DELAY
-				&& Math.abs(data.initialPageX - arrays.tail(data.rollingPageX)) < 30
-				&& Math.abs(data.initialPageY - arrays.tail(data.rollingPageY)) < 30) {
+				&& Math.abs(data.initialPageX - arrays.tail(data.rollingPageX)!) < 30
+				&& Math.abs(data.initialPageY - arrays.tail(data.rollingPageY)!) < 30) {
 
 				const evt = this.newGestureEvent(EventType.Contextmenu, data.initialTarget);
-				evt.pageX = arrays.tail(data.rollingPageX);
-				evt.pageY = arrays.tail(data.rollingPageY);
+				evt.pageX = arrays.tail(data.rollingPageX)!;
+				evt.pageY = arrays.tail(data.rollingPageY)!;
 				this.dispatchEvent(evt);
 
 			} else if (activeTouchCount === 1) {
-				const finalX = arrays.tail(data.rollingPageX);
-				const finalY = arrays.tail(data.rollingPageY);
+				const finalX = arrays.tail(data.rollingPageX)!;
+				const finalY = arrays.tail(data.rollingPageY)!;
 
-				const deltaT = arrays.tail(data.rollingTimestamps) - data.rollingTimestamps[0];
+				const deltaT = arrays.tail(data.rollingTimestamps)! - data.rollingTimestamps[0];
 				const deltaX = finalX - data.rollingPageX[0];
 				const deltaY = finalY - data.rollingPageY[0];
 
@@ -345,8 +345,8 @@ export class Gesture extends Disposable {
 			const data = this.activeTouches[touch.identifier];
 
 			const evt = this.newGestureEvent(EventType.Change, data.initialTarget);
-			evt.translationX = touch.pageX - arrays.tail(data.rollingPageX);
-			evt.translationY = touch.pageY - arrays.tail(data.rollingPageY);
+			evt.translationX = touch.pageX - arrays.tail(data.rollingPageX)!;
+			evt.translationY = touch.pageY - arrays.tail(data.rollingPageY)!;
 			evt.pageX = touch.pageX;
 			evt.pageY = touch.pageY;
 			this.dispatchEvent(evt);
diff --git a/src/vs/base/common/arrays.ts b/src/vs/base/common/arrays.ts
index f8804af0fe72b..c1e97565a1605 100644
--- a/src/vs/base/common/arrays.ts
+++ b/src/vs/base/common/arrays.ts
@@ -13,7 +13,7 @@ import { findFirstIdxMonotonousOrArrLen } from './arraysFind';
  * @param array The array.
  * @param n Which element from the end (default is zero).
  */
-export function tail<T>(array: ArrayLike<T>, n: number = 0): T {
+export function tail<T>(array: ArrayLike<T>, n: number = 0): T | undefined {
 	return array[array.length - (1 + n)];
 }
 
diff --git a/src/vs/workbench/contrib/bulkEdit/browser/bulkFileEdits.ts b/src/vs/workbench/contrib/bulkEdit/browser/bulkFileEdits.ts
index f094897579084..f11d5cb58cdab 100644
--- a/src/vs/workbench/contrib/bulkEdit/browser/bulkFileEdits.ts
+++ b/src/vs/workbench/contrib/bulkEdit/browser/bulkFileEdits.ts
@@ -363,7 +363,7 @@ export class BulkFileEdits {
 		for (let i = 1; i < edits.length; i++) {
 			const edit = edits[i];
 			const lastGroup = tail(groups);
-			if (lastGroup[0].type === edit.type) {
+			if (lastGroup?.[0].type === edit.type) {
 				lastGroup.push(edit);
 			} else {
 				groups.push([edit]);
diff --git a/src/vs/workbench/contrib/inlineChat/browser/inlineChatWidget.ts b/src/vs/workbench/contrib/inlineChat/browser/inlineChatWidget.ts
index d2f77ebf34346..bfd7400f7766c 100644
--- a/src/vs/workbench/contrib/inlineChat/browser/inlineChatWidget.ts
+++ b/src/vs/workbench/contrib/inlineChat/browser/inlineChatWidget.ts
@@ -457,7 +457,7 @@ export class InlineChatWidget {
 		if (!isNonEmptyArray(requests)) {
 			return undefined;
 		}
-		return tail(requests).response?.response.asString();
+		return tail(requests)?.response?.response.asString();
 	}
 
 	getChatModel(): IChatModel {
diff --git a/src/vs/workbench/services/preferences/common/preferencesModels.ts b/src/vs/workbench/services/preferences/common/preferencesModels.ts
index 89022b946b71f..f0c0b5ca0f1c1 100644
--- a/src/vs/workbench/services/preferences/common/preferencesModels.ts
+++ b/src/vs/workbench/services/preferences/common/preferencesModels.ts
@@ -829,7 +829,7 @@ export class DefaultSettingsEditorModel extends AbstractSettingsModel implements
 			.sort((a, b) => a.order - b.order);
 		const nonEmptyResultGroups = resultGroups.filter(group => group.result.filterMatches.length);
 
-		const startLine = tail(this.settingsGroups).range.endLineNumber + 2;
+		const startLine = tail(this.settingsGroups)!.range.endLineNumber + 2;
 		const { settingsGroups: filteredGroups, matches } = this.writeResultGroups(nonEmptyResultGroups, startLine);
 
 		const metadata = this.collectMetadata(resultGroups);