minor polish

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

@@ -137,7 +137,7 @@ export class PanelPart extends CompositePart<Panel> implements IPanelService {
 		const id = viewlet.getId();
 
 		if (this.activePanelContextKey.get() === id) {
-			this.activePanelContextKey.set('');
+			this.activePanelContextKey.reset();
 		}
 	}
 
@@ -301,6 +301,7 @@ export class PanelPart extends CompositePart<Panel> implements IPanelService {
 	}
 
 	dispose(): void {
+		super.dispose();
 		this.disposables = dispose(this.disposables);
 	}
 }

src/vs/workbench/services/viewlet/browser/viewletService.ts

@@ -57,7 +57,7 @@ export class ViewletService implements IViewletService {
 		const id = viewlet.getId();
 
 		if (this.activeViewletContextKey.get() === id) {
-			this.activeViewletContextKey.set('');
+			this.activeViewletContextKey.reset();
 		}
 	}