Converting some parts of panel service to return undefined instead of null

src/vs/workbench/browser/parts/compositePart.ts

@@ -61,7 +61,7 @@ export abstract class CompositePart<T extends Composite> extends Part {
 
 	private mapCompositeToCompositeContainer = new Map<string, HTMLElement>();
 	private mapActionsBindingToComposite = new Map<string, () => void>();
-	private activeComposite: Composite | null;
+	private activeComposite: Composite | undefined;
 	private lastActiveCompositeId: string;
 	private instantiatedCompositeItems: Map<string, CompositeItem>;
 	private titleLabel: ICompositeTitleLabel;
@@ -90,7 +90,6 @@ export abstract class CompositePart<T extends Composite> extends Part {
 	) {
 		super(id, options, themeService, storageService, layoutService);
 
-		this.activeComposite = null;
 		this.instantiatedCompositeItems = new Map<string, CompositeItem>();
 		this.lastActiveCompositeId = storageService.get(activeCompositeSettingsKey, StorageScope.WORKSPACE, this.defaultCompositeId);
 	}
@@ -332,7 +331,7 @@ export abstract class CompositePart<T extends Composite> extends Part {
 		return this.toolBar.setActions(prepareActions(primaryActions), prepareActions(secondaryActions));
 	}
 
-	protected getActiveComposite(): IComposite | null {
+	protected getActiveComposite(): IComposite | undefined {
 		return this.activeComposite;
 	}
 
@@ -346,7 +345,7 @@ export abstract class CompositePart<T extends Composite> extends Part {
 		}
 
 		const composite = this.activeComposite;
-		this.activeComposite = null;
+		this.activeComposite = undefined;
 
 		const compositeContainer = this.mapCompositeToCompositeContainer.get(composite.getId());
 

src/vs/workbench/browser/parts/panel/panelPart.ts

@@ -30,7 +30,7 @@ import { Dimension, trackFocus } from 'vs/base/browser/dom';
 import { localize } from 'vs/nls';
 import { IDisposable } from 'vs/base/common/lifecycle';
 import { IContextKey, IContextKeyService } from 'vs/platform/contextkey/common/contextkey';
-import { isUndefinedOrNull, withUndefinedAsNull, assertIsDefined } from 'vs/base/common/types';
+import { isUndefinedOrNull, assertIsDefined } from 'vs/base/common/types';
 import { ILifecycleService, LifecyclePhase } from 'vs/platform/lifecycle/common/lifecycle';
 import { registerSingleton } from 'vs/platform/instantiation/common/extensions';
 
@@ -218,9 +218,9 @@ export class PanelPart extends CompositePart<Panel> implements IPanelService {
 		}
 	}
 
-	openPanel(id: string, focus?: boolean): Panel | null {
+	openPanel(id: string, focus?: boolean): Panel | undefined {
 		if (this.blockOpeningPanel) {
-			return null; // Workaround against a potential race condition
+			return undefined; // Workaround against a potential race condition
 		}
 
 		// First check if panel is hidden and show if so
@@ -233,7 +233,7 @@ export class PanelPart extends CompositePart<Panel> implements IPanelService {
 			}
 		}
 
-		return withUndefinedAsNull(this.openComposite(id, focus));
+		return this.openComposite(id, focus);
 	}
 
 	showActivity(panelId: string, badge: IBadge, clazz?: string): IDisposable {
@@ -263,7 +263,7 @@ export class PanelPart extends CompositePart<Panel> implements IPanelService {
 		];
 	}
 
-	getActivePanel(): IPanel | null {
+	getActivePanel(): IPanel | undefined {
 		return this.getActiveComposite();
 	}
 

src/vs/workbench/contrib/output/browser/outputServices.ts

@@ -155,7 +155,7 @@ export class OutputService extends Disposable implements IOutputService, ITextMo
 		}
 	}
 
-	private onDidPanelOpen(panel: IPanel | null, preserveFocus: boolean): Promise<void> {
+	private onDidPanelOpen(panel: IPanel | undefined, preserveFocus: boolean): Promise<void> {
 		if (panel && panel.getId() === OUTPUT_PANEL_ID) {
 			this._outputPanel = <OutputPanel>this.panelService.getActivePanel();
 			if (this.activeChannel) {

src/vs/workbench/services/panel/common/panelService.ts

@@ -28,12 +28,12 @@ export interface IPanelService {
 	/**
 	 * Opens a panel with the given identifier and pass keyboard focus to it if specified.
 	 */
-	openPanel(id: string, focus?: boolean): IPanel | null;
+	openPanel(id: string, focus?: boolean): IPanel | undefined;
 
 	/**
 	 * Returns the current active panel or null if none
 	 */
-	getActivePanel(): IPanel | null;
+	getActivePanel(): IPanel | undefined;
 
 	/**
 	 * Returns the panel by id.

src/vs/workbench/test/electron-browser/api/mainThreadDocumentsAndEditors.test.ts

@@ -79,7 +79,7 @@ suite('MainThreadDocumentsAndEditors', () => {
 				onDidPanelOpen = Event.None;
 				onDidPanelClose = Event.None;
 				getActivePanel() {
-					return null;
+					return undefined;
 				}
 			},
 			TestEnvironmentService

src/vs/workbench/test/electron-browser/api/mainThreadEditors.test.ts

@@ -111,7 +111,7 @@ suite('MainThreadEditors', () => {
 				onDidPanelOpen = Event.None;
 				onDidPanelClose = Event.None;
 				getActivePanel() {
-					return null;
+					return undefined;
 				}
 			},
 			TestEnvironmentService

src/vs/workbench/test/workbenchTestServices.ts

@@ -626,8 +626,8 @@ export class TestPanelService implements IPanelService {
 	onDidPanelOpen = new Emitter<{ panel: IPanel, focus: boolean }>().event;
 	onDidPanelClose = new Emitter<IPanel>().event;
 
-	public openPanel(id: string, focus?: boolean): IPanel {
-		return null!;
+	public openPanel(id: string, focus?: boolean): undefined {
+		return undefined;
 	}
 
 	public getPanel(id: string): any {