diff --git a/src/vs/base/test/common/event.test.ts b/src/vs/base/test/common/event.test.ts
index 186f3112ff7..35bae3206a9 100644
--- a/src/vs/base/test/common/event.test.ts
+++ b/src/vs/base/test/common/event.test.ts
@@ -448,7 +448,7 @@ suite('Event utils', () => {
 						e(err);
 					}
 
-					c(null);
+					c(void 0);
 				});
 
 				setTimeout(() => emitter.fire(), 10);
diff --git a/src/vs/workbench/api/node/extHostExtensionService.ts b/src/vs/workbench/api/node/extHostExtensionService.ts
index c5be3ff39e5..236028b92a5 100644
--- a/src/vs/workbench/api/node/extHostExtensionService.ts
+++ b/src/vs/workbench/api/node/extHostExtensionService.ts
@@ -591,7 +591,7 @@ export class ExtHostExtensionService implements ExtHostExtensionServiceShape {
 					if (error) {
 						e(error.toString());
 					} else {
-						c(null);
+						c(void 0);
 					}
 
 					// after tests have run, we shutdown the host
diff --git a/src/vs/workbench/parts/debug/electron-browser/debugService.ts b/src/vs/workbench/parts/debug/electron-browser/debugService.ts
index e696bf302e2..28023df1708 100644
--- a/src/vs/workbench/parts/debug/electron-browser/debugService.ts
+++ b/src/vs/workbench/parts/debug/electron-browser/debugService.ts
@@ -606,7 +606,7 @@ export class DebugService implements IDebugService {
 
 								this.launchOrAttachToSession(session, shouldFocus).then(() => {
 									this._onDidNewSession.fire(session);
-									c(null);
+									c(void 0);
 								}, err => e(err));
 							});
 						});
@@ -727,7 +727,7 @@ export class DebugService implements IDebugService {
 				if (task.isBackground) {
 					return new Promise((c, e) => once(e => e.kind === TaskEventKind.Inactive && e.taskId === task._id, this.taskService.onDidStateChange)(() => {
 						taskStarted = true;
-						c(null);
+						c(void 0);
 					}));
 				}
 
diff --git a/src/vs/workbench/parts/extensions/electron-browser/extensionTipsService.ts b/src/vs/workbench/parts/extensions/electron-browser/extensionTipsService.ts
index 9bdd6f3aa7d..9d2326b8e71 100644
--- a/src/vs/workbench/parts/extensions/electron-browser/extensionTipsService.ts
+++ b/src/vs/workbench/parts/extensions/electron-browser/extensionTipsService.ts
@@ -854,7 +854,7 @@ export class ExtensionTipsService extends Disposable implements IExtensionTipsSe
 
 			fetchPromise = new Promise((c, e) => {
 				setTimeout(() => {
-					Promise.all([this.fetchExecutableRecommendations(), this.fetchDynamicWorkspaceRecommendations()]).then(() => c(null));
+					Promise.all([this.fetchExecutableRecommendations(), this.fetchDynamicWorkspaceRecommendations()]).then(() => c(void 0));
 				}, calledDuringStartup ? 10000 : 0);
 			});
 
diff --git a/src/vs/workbench/parts/extensions/test/electron-browser/extensionsWorkbenchService.test.ts b/src/vs/workbench/parts/extensions/test/electron-browser/extensionsWorkbenchService.test.ts
index fe907d5a032..4fc2046a973 100644
--- a/src/vs/workbench/parts/extensions/test/electron-browser/extensionsWorkbenchService.test.ts
+++ b/src/vs/workbench/parts/extensions/test/electron-browser/extensionsWorkbenchService.test.ts
@@ -1219,7 +1219,7 @@ suite('ExtensionsWorkbenchServiceTest', () => {
 			let counter = 0;
 			event(() => {
 				if (++counter === count) {
-					c(null);
+					c(void 0);
 				}
 			});
 		});
diff --git a/src/vs/workbench/services/configuration/test/electron-browser/configurationEditingService.test.ts b/src/vs/workbench/services/configuration/test/electron-browser/configurationEditingService.test.ts
index 8bd6c1af4f6..86b0a03d1e9 100644
--- a/src/vs/workbench/services/configuration/test/electron-browser/configurationEditingService.test.ts
+++ b/src/vs/workbench/services/configuration/test/electron-browser/configurationEditingService.test.ts
@@ -129,9 +129,9 @@ suite('ConfigurationEditingService', () => {
 	function clearWorkspace(): Promise<void> {
 		return new Promise<void>((c, e) => {
 			if (parentDir) {
-				extfs.del(parentDir, os.tmpdir(), () => c(null), () => c(null));
+				extfs.del(parentDir, os.tmpdir(), () => c(void 0), () => c(void 0));
 			} else {
-				c(null);
+				c(void 0);
 			}
 		}).then(() => parentDir = null);
 	}
diff --git a/src/vs/workbench/services/keybinding/test/electron-browser/keybindingEditing.test.ts b/src/vs/workbench/services/keybinding/test/electron-browser/keybindingEditing.test.ts
index 7ea35c1411f..75dc0ad53da 100644
--- a/src/vs/workbench/services/keybinding/test/electron-browser/keybindingEditing.test.ts
+++ b/src/vs/workbench/services/keybinding/test/electron-browser/keybindingEditing.test.ts
@@ -111,9 +111,9 @@ suite('KeybindingsEditing', () => {
 	teardown(() => {
 		return new Promise<void>((c, e) => {
 			if (testDir) {
-				extfs.del(testDir, os.tmpdir(), () => c(null), () => c(null));
+				extfs.del(testDir, os.tmpdir(), () => c(void 0), () => c(void 0));
 			} else {
-				c(null);
+				c(void 0);
 			}
 		}).then(() => testDir = null);
 	});
diff --git a/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts b/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts
index b19dac9a834..ea197548491 100644
--- a/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts
+++ b/src/vs/workbench/test/electron-browser/api/extHostTreeViews.test.ts
@@ -219,7 +219,7 @@ suite('ExtHostTreeView', function () {
 					label: { label: 'b' },
 					collapsibleState: TreeItemCollapsibleState.Collapsed
 				});
-				c(null);
+				c(void 0);
 			});
 			onDidChangeTreeNode.fire(getNode('b'));
 		});