diff --git a/projects/scion/workbench/src/lib/activity-part/activity-part.component.ts b/projects/scion/workbench/src/lib/activity-part/activity-part.component.ts
index 8613988af..7faccad24 100644
--- a/projects/scion/workbench/src/lib/activity-part/activity-part.component.ts
+++ b/projects/scion/workbench/src/lib/activity-part/activity-part.component.ts
@@ -52,9 +52,6 @@ export class ActivityPartComponent {
   private _panelWidth = PANEL_INITIAL_WIDTH;
   private _panelWidth$ = new Subject<number>();
 
-  @ViewChild('viewport')
-  public viewport!: ElementRef;
-
   @ViewChild('panel', {read: ElementRef})
   private _panelElementRef!: ElementRef;
 
diff --git a/projects/scion/workbench/src/lib/activity-part/activity.ts b/projects/scion/workbench/src/lib/activity-part/activity.ts
index 68daf8a6b..c62121fd7 100644
--- a/projects/scion/workbench/src/lib/activity-part/activity.ts
+++ b/projects/scion/workbench/src/lib/activity-part/activity.ts
@@ -14,43 +14,43 @@ export abstract class Activity {
   /**
    * Specifies the title of the activity.
    */
-  public title?: string;
+  public abstract title: string | null;
 
   /**
    * Specifies CSS class(es) added to the activity item and activity panel, e.g. used for e2e testing.
    */
-  public cssClass?: string | string[];
+  public abstract cssClass: string | string[] | undefined;
 
   /**
    * Specifies the text for the activity item.
    *
    * You can use it in combination with `itemCssClass`, e.g. to render an icon glyph by using its textual name.
    */
-  public itemText?: string;
+  public abstract itemText: string | null;
 
   /**
    * Specifies CSS class(es) added to the activity item, e.g. used for e2e testing or to set an icon font class.
    */
-  public itemCssClass?: string | string[];
+  public abstract itemCssClass: string | string[] | undefined;
   /**
    * Controls whether to open this activity in the activity panel or to open it in a separate view.
    */
-  public target?: 'activity-panel' | 'view';
+  public abstract target: 'activity-panel' | 'view';
 
   /**
    * Controls whether to show or hide this activity. By default, this activity is showing.
    */
-  public visible?: boolean;
+  public abstract visible: boolean;
 
   /**
    * Specifies where to insert this activity in the list of activities.
    */
-  public position?: number;
+  public abstract position: number | undefined;
 
   /**
    * Specifies the number of pixels added to the activity panel width if this is the active activity.
    */
-  public panelWidthDelta?: number;
+  public abstract panelWidthDelta: number;
 
   /**
    * Specifies the routing commands used by Angular router to navigate when this activity is activated.
@@ -99,15 +99,15 @@ export class InternalActivity implements Activity {
   private _active$ = new BehaviorSubject<boolean>(false);
 
   public panelWidthDelta = 0;
-  public title?: string;
-  public cssClass?: string | string[];
+  public title: string | null = null;
+  public cssClass: string | string[] | undefined;
 
-  public itemText?: string;
-  public itemCssClass?: string | string[];
+  public itemText: string | null = null;
+  public itemCssClass: string | string[] | undefined;
 
   public target: 'activity-panel' | 'view' = 'activity-panel';
   public visible = true;
-  public position?: number;
+  public position: number | undefined;
 
   constructor(private _wbRouter: WorkbenchRouter, private _injector: Injector) {
   }
diff --git a/projects/scion/workbench/src/lib/activity-part/wb-activity-action.directive.ts b/projects/scion/workbench/src/lib/activity-part/wb-activity-action.directive.ts
index 6696dbe9c..803b1a737 100644
--- a/projects/scion/workbench/src/lib/activity-part/wb-activity-action.directive.ts
+++ b/projects/scion/workbench/src/lib/activity-part/wb-activity-action.directive.ts
@@ -10,7 +10,6 @@
 
 import { Directive, OnDestroy, TemplateRef } from '@angular/core';
 import { WorkbenchActivityPartService } from './workbench-activity-part.service';
-import { Activity } from './activity';
 import { ActivatedRoute } from '@angular/router';
 import { Disposable } from '../disposable';
 
@@ -34,18 +33,17 @@ import { Disposable } from '../disposable';
 })
 export class WbActivityActionDirective implements OnDestroy {
 
-  private readonly _activity: Activity | null;
   private readonly _action: Disposable;
 
   constructor(private _template: TemplateRef<void>,
               activityService: WorkbenchActivityPartService,
               route: ActivatedRoute) {
-    this._activity = activityService.getActivityFromRoutingContext(route.snapshot);
-    if (!this._activity) {
+    const activity = activityService.getActivityFromRoutingContext(route.snapshot);
+    if (!activity) {
       throw Error('[RoutingContextError] Route not in the context of an activity');
     }
 
-    this._action = this._activity.registerAction(this._template);
+    this._action = activity.registerAction(this._template);
   }
 
   public ngOnDestroy(): void {
diff --git a/projects/scion/workbench/src/lib/activity-part/wb-activity.directive.ts b/projects/scion/workbench/src/lib/activity-part/wb-activity.directive.ts
index a80327954..5d0f6a6cb 100644
--- a/projects/scion/workbench/src/lib/activity-part/wb-activity.directive.ts
+++ b/projects/scion/workbench/src/lib/activity-part/wb-activity.directive.ts
@@ -37,7 +37,7 @@ export class WbActivityDirective implements OnInit, OnDestroy {
    * Specifies the title of the activity.
    */
   @Input()
-  public set title(title: string) {
+  public set title(title: string | null) {
     this.activity.title = title;
   }
 
@@ -47,7 +47,7 @@ export class WbActivityDirective implements OnInit, OnDestroy {
    * You can use it in combination with `itemCssClass`, e.g. to render an icon glyph by using its textual name.
    */
   @Input()
-  public set itemText(itemText: string) {
+  public set itemText(itemText: string | null) {
     this.activity.itemText = itemText;
   }
 
@@ -55,7 +55,7 @@ export class WbActivityDirective implements OnInit, OnDestroy {
    * Specifies CSS class(es) added to the activity item, e.g. used for e2e testing or to set an icon font class.
    */
   @Input()
-  public set itemCssClass(itemCssClass: string | string[]) {
+  public set itemCssClass(itemCssClass: string | string[] | undefined) {
     this.activity.itemCssClass = itemCssClass;
   }
 
@@ -63,7 +63,7 @@ export class WbActivityDirective implements OnInit, OnDestroy {
    * Specifies CSS class(es) added to the activity item and activity panel, e.g. used for e2e testing.
    */
   @Input()
-  public set cssClass(cssClass: string | string[]) {
+  public set cssClass(cssClass: string | string[] | undefined) {
     this.activity.cssClass = cssClass;
   }
 
diff --git a/projects/scion/workbench/src/lib/dom.util.ts b/projects/scion/workbench/src/lib/dom.util.ts
index 01123be5a..8dabc8ae6 100644
--- a/projects/scion/workbench/src/lib/dom.util.ts
+++ b/projects/scion/workbench/src/lib/dom.util.ts
@@ -17,7 +17,8 @@ export function createElement(tag: string, options: ElementCreateOptions): HTMLE
 /**
  * Applies the given style(s) to the given element.
  *
- * To unset a style property provide `null` as its value.
+ * Specify styles to be modified by passing a dictionary containing CSS property names (hyphen case).
+ * To remove a style, set its value to `null`.
  */
 export function setStyle(element: HTMLElement | ElementRef<HTMLElement>, style: { [style: string]: any | null }): void {
   const target = coerceElement(element);
diff --git a/projects/scion/workbench/src/lib/layout/parts-layout.component.ts b/projects/scion/workbench/src/lib/layout/parts-layout.component.ts
index c798551ac..50003a7d1 100644
--- a/projects/scion/workbench/src/lib/layout/parts-layout.component.ts
+++ b/projects/scion/workbench/src/lib/layout/parts-layout.component.ts
@@ -55,12 +55,12 @@ export class PartsLayoutComponent implements OnInit, OnDestroy {
   /**
    * Reference to the root part of the layout. Is only set if the layout root is of the type {@link MPart}.
    */
-  public rootPart!: WbComponentPortal<ViewPartComponent> | null;
+  public rootPart: WbComponentPortal<ViewPartComponent> | null = null;
 
   /**
    * Reference to the root node of the layout. Is only set if the layout root is of the type {@link MTreeNode}.
    */
-  public rootNode!: MTreeNode | null;
+  public rootNode: MTreeNode | null = null;
 
   constructor(private _viewPartRegistry: WorkbenchViewPartRegistry,
               private _layoutService: WorkbenchLayoutService,
@@ -74,7 +74,7 @@ export class PartsLayoutComponent implements OnInit, OnDestroy {
         pairwise(),
         takeUntil(this._destroy$),
       )
-      .subscribe(([prevLayout, curLayout]: [PartsLayout, PartsLayout]) => {
+      .subscribe(([prevLayout, curLayout]: [PartsLayout | null, PartsLayout]) => {
         // Determine the parts which are about to be re-parented in the DOM, and detach them temporarily from the Angular component tree,
         // so that they are not destroyed when being re-parented.
         const reattachFn = this.detachPortalsToBeMovedFromComponentTree(prevLayout, curLayout);
@@ -98,22 +98,29 @@ export class PartsLayoutComponent implements OnInit, OnDestroy {
    *
    * Returns a function to attach the detached portals to the Angular component tree anew.
    */
-  private detachPortalsToBeMovedFromComponentTree(prevLayout: PartsLayout, newLayout: PartsLayout): () => void {
+  private detachPortalsToBeMovedFromComponentTree(prevLayout: PartsLayout | null, currLayout: PartsLayout): () => void {
     if (!prevLayout) {
       return noop; // no current layout in place, so no portal is moved
     }
 
     // For each part, compute its path in the layout tree. The path is the list of all parent node ids.
-    const newPartPaths: Map<string, string[]> = newLayout.parts.reduce((acc, part) => {
+    const currPartPathsByPartId: Map<string, string[]> = currLayout.parts.reduce((acc, part) => {
       return acc.set(part.partId, part.getPath());
     }, new Map<string, string[]>());
 
     // Determine parts to be moved in the layout tree.
     const partPortalsToBeMoved: WbComponentPortal<ViewPartComponent>[] = prevLayout.parts.reduce((acc, prevPart) => {
-      const prevPartPath = prevPart.getPath();
-      const newPartPath = newPartPaths.get(prevPart.partId)!;
+      const prevPartPath: string[] = prevPart.getPath();
+      const currPartPath: string[] | undefined = currPartPathsByPartId.get(prevPart.partId);
 
-      if (!Arrays.isEqual(newPartPath, prevPartPath)) {
+      // If the part is no longer contained in the layout but is still present in the parts registry, detach it so that its views
+      // will not get destroyed when applying the new layout, i.e., when moving all its views to another part.
+      if (!currPartPath) {
+        return acc.concat(this._viewPartRegistry.getElseNull(prevPart.partId)?.portal || []);
+      }
+
+      // If the part is moved in the layout, detach it to not destroy its views.
+      if (!Arrays.isEqual(currPartPath, prevPartPath)) {
         return acc.concat(this._viewPartRegistry.getElseThrow(prevPart.partId).portal);
       }
       return acc;
diff --git a/projects/scion/workbench/src/lib/layout/parts-layout.ts b/projects/scion/workbench/src/lib/layout/parts-layout.ts
index a85fec9e9..105f576c3 100644
--- a/projects/scion/workbench/src/lib/layout/parts-layout.ts
+++ b/projects/scion/workbench/src/lib/layout/parts-layout.ts
@@ -208,7 +208,7 @@ export class PartsLayout {
    */
   public serialize(options: { nullIfEmpty: false }): string;
   public serialize(options?: { nullIfEmpty?: true } | {}): string | null;
-  public serialize(options?: { nullIfEmpty?: boolean }): string | null{
+  public serialize(options?: { nullIfEmpty?: boolean }): string | null {
     if ((options?.nullIfEmpty ?? true) && this._root instanceof MPart && this._root.isEmpty()) {
       return null;
     }
@@ -264,13 +264,12 @@ export class PartsLayout {
   private _removePart(partId: string): this {
     assertNotNullish(partId, {orElseThrow: () => Error(`[PartsLayoutError] PartId must not be 'null' or 'undefined'.`)});
 
-    const part = this._findPart(partId, {orElseThrow: true});
-
     // The last part is never removed.
     if (this.parts.length === 1) {
       return this;
     }
 
+    const part = this._findPart(partId, {orElseThrow: true});
     const partIndex = this.parts.indexOf(part);
     const siblingElement = (part.parent!.child1 === part ? part.parent!.child2 : part.parent!.child1);
     if (!part.parent!.parent) {
diff --git a/projects/scion/workbench/src/lib/layout/workbench-layout.service.ts b/projects/scion/workbench/src/lib/layout/workbench-layout.service.ts
index e797a1cff..f4f436fcd 100644
--- a/projects/scion/workbench/src/lib/layout/workbench-layout.service.ts
+++ b/projects/scion/workbench/src/lib/layout/workbench-layout.service.ts
@@ -47,9 +47,9 @@ export class WorkbenchLayoutService {
    */
   public readonly layout$: Observable<PartsLayout> = this._layoutChange$
     .pipe(
-      startWith(null! as PartsLayout),
-      map(() => this.layout),
-      filter((layout): layout is PartsLayout => Boolean(layout)),
+      startWith(undefined as void),
+      map<void, PartsLayout | null>(() => this.layout),
+      filter((layout: PartsLayout | null): layout is PartsLayout => layout !== null),
     );
 
   constructor(viewDragService: ViewDragService, private _zone: NgZone) {
@@ -95,7 +95,7 @@ export class WorkbenchLayoutService {
    * Returns a reference to current {@link PartsLayout}, if any. Is `null` until the initial navigation is performed.
    */
   public get layout(): PartsLayout | null {
-    return this._layout || null;
+    return this._layout;
   }
 
   /**
diff --git a/projects/scion/workbench/src/lib/logging/logger.ts b/projects/scion/workbench/src/lib/logging/logger.ts
index 2eb7eb464..0916bcdb3 100644
--- a/projects/scion/workbench/src/lib/logging/logger.ts
+++ b/projects/scion/workbench/src/lib/logging/logger.ts
@@ -12,7 +12,9 @@ import { Inject, Injectable, OnDestroy, Optional } from '@angular/core';
 import { NavigationStart, ParamMap, Router, RouterEvent } from '@angular/router';
 import { filter, map, startWith, takeUntil } from 'rxjs/operators';
 import { Observable, Subject } from 'rxjs';
-import { LogAppender, LogEvent, LoggerName, LogLevel, LogLevelStrings } from './logging.model';
+import { LogAppender, LogEvent, LoggerName, LogLevel } from './logging.model';
+
+type LogLevelStrings = keyof typeof LogLevel;
 
 /**
  * Logger used by the workbench to log messages.
@@ -130,8 +132,8 @@ export class ɵLogger implements Logger, OnDestroy {  // tslint:disable-line:cla
         startWith(router.url),
         filter((event): event is NavigationStart => event instanceof NavigationStart),
         map<RouterEvent, ParamMap>(routerEvent => router.parseUrl(routerEvent.url).queryParamMap),
-        map(queryParamMap => queryParamMap.get('loglevel')?.toUpperCase() as LogLevelStrings),
-        map(logLevelRaw => logLevelRaw ? LogLevel[logLevelRaw] : undefined),
+        map(queryParamMap => queryParamMap.get('loglevel')?.toUpperCase() as LogLevelStrings | undefined),
+        map(logLevelString => logLevelString ? LogLevel[logLevelString] : undefined),
       );
   }
 
diff --git a/projects/scion/workbench/src/lib/logging/logging.model.ts b/projects/scion/workbench/src/lib/logging/logging.model.ts
index 7e6561e98..5544fc671 100644
--- a/projects/scion/workbench/src/lib/logging/logging.model.ts
+++ b/projects/scion/workbench/src/lib/logging/logging.model.ts
@@ -16,7 +16,6 @@ import { Injectable } from '@angular/core';
 export enum LogLevel {
   DEBUG, INFO, WARN, ERROR
 }
-export type LogLevelStrings = keyof typeof LogLevel;
 
 /**
  * Provides information about a message to be logged.
diff --git a/projects/scion/workbench/src/lib/message-box/message-box.component.ts b/projects/scion/workbench/src/lib/message-box/message-box.component.ts
index 0d2bdf04d..9bdbd958e 100644
--- a/projects/scion/workbench/src/lib/message-box/message-box.component.ts
+++ b/projects/scion/workbench/src/lib/message-box/message-box.component.ts
@@ -36,16 +36,16 @@ export class MessageBoxComponent implements OnInit, OnDestroy {
   private _cancelBlinkTimer$ = new Subject<void>();
   private _activeActionButton: HTMLElement | undefined;
 
-  public portal!: ComponentPortal<any>;
+  public portal: ComponentPortal<any> | undefined;
 
   @HostBinding('style.transform')
-  public transform!: string;
+  public transform: string | undefined;
 
   @HostBinding('class.blinking')
-  public blinking!: boolean;
+  public blinking = false;
 
   @HostBinding('class.text-selectable')
-  public textSelectable!: boolean;
+  public textSelectable = false;
 
   @HostBinding('attr.tabindex')
   public tabindex = -1;
diff --git a/projects/scion/workbench/src/lib/message-box/message-box.service.ts b/projects/scion/workbench/src/lib/message-box/message-box.service.ts
index 7abcf3913..8642a2e70 100644
--- a/projects/scion/workbench/src/lib/message-box/message-box.service.ts
+++ b/projects/scion/workbench/src/lib/message-box/message-box.service.ts
@@ -46,7 +46,7 @@ export class MessageBoxService implements OnDestroy {
 
   private _destroy$ = new Subject<void>();
   private _messageBoxes$ = new BehaviorSubject<ɵMessageBox[]>([]);
-  private _messageBoxServiceHierarchy: MessageBoxService[];
+  private _messageBoxServiceHierarchy: [MessageBoxService, ...MessageBoxService[]]; // minItems: 1
 
   constructor(@Optional() @SkipSelf() private _parentMessageBoxService: MessageBoxService,
               @Optional() private _view: WorkbenchView,
@@ -133,13 +133,13 @@ export class MessageBoxService implements OnDestroy {
   /**
    * Returns the message box service hierarchy.
    */
-  private computeMessageBoxServiceHierarchy(): MessageBoxService[] {
+  private computeMessageBoxServiceHierarchy(): [MessageBoxService, ...MessageBoxService[]] {
     const hierarchy: MessageBoxService[] = [];
     let current: MessageBoxService = this;
     do {
       hierarchy.push(current);
     } while ((current = current._parentMessageBoxService)); // tslint:disable-line:no-conditional-assignment
-    return hierarchy;
+    return hierarchy as [MessageBoxService, ...MessageBoxService[]];
   }
 
   /**
diff --git a/projects/scion/workbench/src/lib/message-box/move.directive.ts b/projects/scion/workbench/src/lib/message-box/move.directive.ts
index e32f1d48e..c2cf5275a 100644
--- a/projects/scion/workbench/src/lib/message-box/move.directive.ts
+++ b/projects/scion/workbench/src/lib/message-box/move.directive.ts
@@ -20,8 +20,8 @@ import { first, takeUntil } from 'rxjs/operators';
 export class MoveDirective implements OnDestroy {
 
   private _destroy$ = new Subject<void>();
-  private _x!: number;
-  private _y!: number;
+  private _x = 0;
+  private _y = 0;
 
   @Output()
   public wbMoveStart = new EventEmitter<void>();
diff --git a/projects/scion/workbench/src/lib/microfrontend-platform/initialization/microfrontend-platform-initializer.service.ts b/projects/scion/workbench/src/lib/microfrontend-platform/initialization/microfrontend-platform-initializer.service.ts
index 37f087289..22a46377f 100644
--- a/projects/scion/workbench/src/lib/microfrontend-platform/initialization/microfrontend-platform-initializer.service.ts
+++ b/projects/scion/workbench/src/lib/microfrontend-platform/initialization/microfrontend-platform-initializer.service.ts
@@ -25,7 +25,7 @@ import { LogDelegate } from './log-delegate.service';
 @Injectable()
 export class MicrofrontendPlatformInitializer implements WorkbenchInitializer, OnDestroy {
 
-  private _hostAppConfigIfAbsent!: ApplicationConfig | null;
+  private _syntheticHostAppConfig: ApplicationConfig | null = null;
 
   constructor(private _workbenchModuleConfig: WorkbenchModuleConfig,
               private _microfrontendPlatformConfigLoader: MicrofrontendPlatformConfigLoader,
@@ -44,13 +44,13 @@ export class MicrofrontendPlatformInitializer implements WorkbenchInitializer, O
     const microfrontendPlatformConfig = await this._microfrontendPlatformConfigLoader.load();
 
     // Create a synthetic app config for the workbench host if not passed in the app list.
-    this._hostAppConfigIfAbsent = this.createHostAppConfigIfAbsent(microfrontendPlatformConfig);
+    this._syntheticHostAppConfig = this.createSyntheticHostAppConfigIfAbsent(microfrontendPlatformConfig);
 
     // Assemble the effective microfrontend platform config.
-    const effectiveHostSymbolicName = this._hostAppConfigIfAbsent?.symbolicName || this._workbenchModuleConfig.microfrontends?.platformHost?.symbolicName!;
+    const effectiveHostSymbolicName = this._syntheticHostAppConfig?.symbolicName || this._workbenchModuleConfig.microfrontends!.platformHost!.symbolicName!;
     const effectiveMicrofrontendPlatformConfig: PlatformConfig = {
       ...microfrontendPlatformConfig,
-      apps: microfrontendPlatformConfig.apps.concat(this._hostAppConfigIfAbsent || []),
+      apps: microfrontendPlatformConfig.apps.concat(this._syntheticHostAppConfig || []),
     };
 
     // Enable the API to register intentions at runtime, required for microfrontend routing to register the wildcard `view` intention.
@@ -93,17 +93,17 @@ export class MicrofrontendPlatformInitializer implements WorkbenchInitializer, O
    * Regarding the manifest URL, we create an object URL for the manifest object as passed to the workbench module config,
    * or use an empty manifest if absent.
    */
-  private createHostAppConfigIfAbsent(microfrontendPlatformConfig: PlatformConfig): ApplicationConfig | null {
+  private createSyntheticHostAppConfigIfAbsent(microfrontendPlatformConfig: PlatformConfig): ApplicationConfig | null {
     // Do nothing if the host config is present in the app list.
-    const hostSymbolicName = this._workbenchModuleConfig.microfrontends?.platformHost?.symbolicName;
+    const hostSymbolicName = this._workbenchModuleConfig.microfrontends!.platformHost?.symbolicName;
     if (microfrontendPlatformConfig.apps.some(app => app.symbolicName === hostSymbolicName)) {
       return null;
     }
 
     // Get the manifest object passed to the workbench module config, or create an empty manifest if absent.
-    const hostManifest: ApplicationManifest = this._workbenchModuleConfig.microfrontends?.platformHost?.manifest || {name: 'Workbench Host'};
+    const hostManifest: ApplicationManifest = this._workbenchModuleConfig.microfrontends!.platformHost?.manifest || {name: 'Workbench Host'};
     return {
-      symbolicName: this._workbenchModuleConfig.microfrontends?.platformHost?.symbolicName || 'workbench-host',
+      symbolicName: this._workbenchModuleConfig.microfrontends!.platformHost?.symbolicName || 'workbench-host',
       manifestUrl: URL.createObjectURL(new Blob([JSON.stringify(hostManifest)], {type: 'application/json'})),
     };
   }
@@ -121,6 +121,6 @@ export class MicrofrontendPlatformInitializer implements WorkbenchInitializer, O
   }
 
   public ngOnDestroy(): void {
-    this._hostAppConfigIfAbsent && URL.revokeObjectURL(this._hostAppConfigIfAbsent.manifestUrl);
+    this._syntheticHostAppConfig && URL.revokeObjectURL(this._syntheticHostAppConfig.manifestUrl);
   }
 }
diff --git a/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-popup/microfrontend-popup-command-handler.service.ts b/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-popup/microfrontend-popup-command-handler.service.ts
index d832bf341..73f3bed5d 100644
--- a/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-popup/microfrontend-popup-command-handler.service.ts
+++ b/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-popup/microfrontend-popup-command-handler.service.ts
@@ -24,6 +24,7 @@ import { ROUTER_OUTLET_NAME } from '../../workbench.constants';
 import { Router } from '@angular/router';
 import { WbRouterOutletComponent } from '../../routing/wb-router-outlet.component';
 import { RouterUtils } from '../../routing/router.util';
+import { Commands } from '../../routing/workbench-router.service';
 
 /**
  * Handles microfrontend popup commands, instructing the Workbench {@link PopupService} to navigate to the microfrontend of a given popup capability.
@@ -40,7 +41,7 @@ export class MicrofrontendPopupCommandHandler {
               private _router: Router,
               private _zone: NgZone,
               {symbolicName: hostAppSymbolicName}: MicroApplicationConfig) {
-    this._messageClient.onMessage<ɵWorkbenchPopupCommand>(ɵWorkbenchCommands.popup, async (message) => {
+    this._messageClient.onMessage<ɵWorkbenchPopupCommand>(ɵWorkbenchCommands.popup, async message => {
       const command = message.body!;
       this._logger.debug(() => 'Handling microfrontend popup command', LoggerNames.MICROFRONTEND, command);
 
@@ -165,8 +166,8 @@ export class MicrofrontendPopupCommandHandler {
     // Replace placeholders with the values of the qualifier and params, if any.
     path = RouterUtils.substituteNamedParameters(path, extras.params);
 
-    const outletCommands = path !== null ? RouterUtils.segmentsToCommands(RouterUtils.parsePath(this._router, path)) : null;
-    const commands = [{outlets: {[extras.outletName]: outletCommands}}];
+    const outletCommands: Commands | null = (path !== null ? RouterUtils.segmentsToCommands(RouterUtils.parsePath(this._router, path)) : null);
+    const commands: Commands = [{outlets: {[extras.outletName]: outletCommands}}];
     return this._router.navigate(commands, {skipLocationChange: true, queryParamsHandling: 'merge'});
   }
 }
diff --git a/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-view/microfrontend-view.component.ts b/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-view/microfrontend-view.component.ts
index b100dd9e2..0aa1725a0 100644
--- a/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-view/microfrontend-view.component.ts
+++ b/projects/scion/workbench/src/lib/microfrontend-platform/microfrontend-view/microfrontend-view.component.ts
@@ -255,9 +255,6 @@ export class MicrofrontendViewComponent implements OnInit, OnDestroy, WbBeforeDe
   }
 }
 
-/**
- * @internal
- */
 interface WorkbenchViewCapabilityWithParams {
   capability?: WorkbenchViewCapability;
   params: Params;
diff --git a/projects/scion/workbench/src/lib/microfrontend-platform/workbench-microfrontend-support.ts b/projects/scion/workbench/src/lib/microfrontend-platform/workbench-microfrontend-support.ts
index fc87e80ab..77f5b5674 100644
--- a/projects/scion/workbench/src/lib/microfrontend-platform/workbench-microfrontend-support.ts
+++ b/projects/scion/workbench/src/lib/microfrontend-platform/workbench-microfrontend-support.ts
@@ -79,7 +79,7 @@ class MicrofrontendPlatformModuleConfigLoader implements MicrofrontendPlatformCo
   }
 
   public load(): Promise<PlatformConfig> {
-    return Promise.resolve(this._workbenchModuleConfig.microfrontends?.platform as PlatformConfig);
+    return Promise.resolve(this._workbenchModuleConfig.microfrontends!.platform as PlatformConfig);
   }
 }
 
diff --git a/projects/scion/workbench/src/lib/notification/notification.component.ts b/projects/scion/workbench/src/lib/notification/notification.component.ts
index 447af44de..739d37e52 100644
--- a/projects/scion/workbench/src/lib/notification/notification.component.ts
+++ b/projects/scion/workbench/src/lib/notification/notification.component.ts
@@ -31,7 +31,7 @@ export class NotificationComponent implements OnChanges, OnDestroy {
   private _destroy$ = new Subject<void>();
   private _closeTimerChange$ = new Subject<void>();
 
-  public portal!: ComponentPortal<any>;
+  public portal: ComponentPortal<any> | undefined;
 
   @Input()
   public notification!: ɵNotification;
diff --git a/projects/scion/workbench/src/lib/popup/popup.component.ts b/projects/scion/workbench/src/lib/popup/popup.component.ts
index 1123eed2f..15406ddfb 100644
--- a/projects/scion/workbench/src/lib/popup/popup.component.ts
+++ b/projects/scion/workbench/src/lib/popup/popup.component.ts
@@ -28,33 +28,33 @@ export class PopupComponent {
   public portal: ComponentPortal<any>;
 
   @HostBinding('style.width')
-  public get popupWidth(): string | null {
-    return this._popupConfig.size?.width ?? null;
+  public get popupWidth(): string | undefined {
+    return this._popupConfig.size?.width;
   }
 
   @HostBinding('style.min-width')
-  public get popupMinWidth(): string | null {
-    return this._popupConfig.size?.minWidth ?? null;
+  public get popupMinWidth(): string | undefined {
+    return this._popupConfig.size?.minWidth;
   }
 
   @HostBinding('style.max-width')
-  public get popupMaxWidth(): string | null {
-    return this._popupConfig.size?.maxWidth ?? null;
+  public get popupMaxWidth(): string | undefined {
+    return this._popupConfig.size?.maxWidth;
   }
 
   @HostBinding('style.height')
-  public get popupHeight(): string | null {
-    return this._popupConfig.size?.height ?? null;
+  public get popupHeight(): string | undefined {
+    return this._popupConfig.size?.height;
   }
 
   @HostBinding('style.min-height')
-  public get popupMinHeight(): string | null {
-    return this._popupConfig.size?.minHeight ?? null;
+  public get popupMinHeight(): string | undefined {
+    return this._popupConfig.size?.minHeight;
   }
 
   @HostBinding('style.max-height')
-  public get popupMaxHeight(): string | null {
-    return this._popupConfig.size?.maxHeight ?? null;
+  public get popupMaxHeight(): string | undefined {
+    return this._popupConfig.size?.maxHeight;
   }
 
   constructor(private _popupConfig: PopupConfig, injector: Injector) {
diff --git a/projects/scion/workbench/src/lib/popup/popup.config.ts b/projects/scion/workbench/src/lib/popup/popup.config.ts
index 46efed0fa..b1c742d3b 100644
--- a/projects/scion/workbench/src/lib/popup/popup.config.ts
+++ b/projects/scion/workbench/src/lib/popup/popup.config.ts
@@ -29,14 +29,14 @@ export abstract class PopupConfig {
    *
    * The align setting can be used to further control where the popup opens relative to its anchor.
    */
-  public readonly anchor!: ElementRef<Element> | Element | PopupOrigin | Observable<PopupOrigin>;
+  public abstract readonly anchor: ElementRef<Element> | Element | PopupOrigin | Observable<PopupOrigin>;
   /**
    * Specifies the component to display in the popup.
    *
    * In the component, you can inject the popup handle {@link Popup} to interact with the popup, such as to close it
    * or obtain its input data.
    */
-  public readonly component!: Type<any>;
+  public abstract readonly component: Type<any>;
   /**
    * Instructs Angular how to construct the component. In most cases, construct options need not to be set.
    */
@@ -179,12 +179,12 @@ export abstract class Popup<T = any> {
   /**
    * Input data as passed by the popup opener when opened the popup, or `undefined` if not passed.
    */
-  public readonly input: T | undefined;
+  public abstract readonly input: T | undefined;
 
   /**
    * Preferred popup size as specified by the popup opener, or `undefined` if not set.
    */
-  public readonly size: PopupSize | undefined;
+  public abstract readonly size: PopupSize | undefined;
 
   /**
    * Closes the popup. Optionally, pass a result to the popup opener.
diff --git a/projects/scion/workbench/src/lib/portal/wb-component-portal.ts b/projects/scion/workbench/src/lib/portal/wb-component-portal.ts
index 4d1e2b55f..460c6843f 100644
--- a/projects/scion/workbench/src/lib/portal/wb-component-portal.ts
+++ b/projects/scion/workbench/src/lib/portal/wb-component-portal.ts
@@ -81,7 +81,7 @@ export class WbComponentPortal<T> {
 
     this.detachFromComponentTree();
     this._viewContainerRef = viewContainerRef;
-    this._portalInjector.elementInjector = this.viewContainerRef ? this.viewContainerRef.injector : null;
+    this._portalInjector.elementInjector = this.viewContainerRef ? this.viewContainerRef.injector : Injector.NULL;
     this.attachToComponentTree();
   }
 
@@ -129,19 +129,22 @@ export class WbComponentPortal<T> {
    * Destroys the component instance and all of the data structures associated with it.
    */
   public destroy(): void {
-    this._componentRef!.destroy();
+    this.componentRef.destroy();
   }
 
   public get componentRef(): ComponentRef<T> {
-    return this._componentRef!;
+    if (!this._componentRef) {
+      throw Error('[PortalError] Illegal state: Portal already destroyed.');
+    }
+    return this._componentRef;
   }
 
-  public get viewContainerRef(): ViewContainerRef {
-    return this._viewContainerRef!;
+  public get viewContainerRef(): ViewContainerRef | null {
+    return this._viewContainerRef;
   }
 
   public get isAttached(): boolean {
-    return this._viewContainerRef && this._viewContainerRef.indexOf(this._componentRef!.hostView) > -1 || false;
+    return this._componentRef && this._viewContainerRef && this._viewContainerRef.indexOf(this._componentRef.hostView) > -1 || false;
   }
 
   public get isDestroyed(): boolean {
@@ -182,7 +185,7 @@ export interface PortalConfig {
  */
 class WbPortalInjector implements Injector {
 
-  constructor(private _customTokens: WeakMap<any, any>, public elementInjector: Injector | null) {
+  constructor(private _customTokens: WeakMap<any, any>, public elementInjector: Injector) {
   }
 
   public get<T>(token: Type<T> | InjectionToken<T>, notFoundValue?: T, flags?: InjectFlags): T {
@@ -208,6 +211,6 @@ class WbPortalInjector implements Injector {
      *  - el1.injector.get(token, NOT_FOUND_CHECK_ONLY_ELEMENT_INJECTOR) -> do not check the module
      *  - mod2.injector.get(token, default)
      */
-    return (this.elementInjector || Injector.NULL).get(token, notFoundValue, flags);
+    return this.elementInjector.get(token, notFoundValue, flags);
   }
 }
diff --git a/projects/scion/workbench/src/lib/portal/wb-portal-outlet.component.ts b/projects/scion/workbench/src/lib/portal/wb-portal-outlet.component.ts
index 152766b0d..a15253ce8 100644
--- a/projects/scion/workbench/src/lib/portal/wb-portal-outlet.component.ts
+++ b/projects/scion/workbench/src/lib/portal/wb-portal-outlet.component.ts
@@ -18,7 +18,7 @@ import { WbComponentPortal } from './wb-component-portal';
 })
 export class WbPortalOutletComponent implements OnDestroy {
 
-  private _portal!: WbComponentPortal<any>;
+  private _portal: WbComponentPortal<any> | undefined;
 
   @ViewChild(TemplateRef, {read: ViewContainerRef, static: true})
   private _viewContainerRef!: ViewContainerRef;
diff --git a/projects/scion/workbench/src/lib/routing/wb-router-link.directive.ts b/projects/scion/workbench/src/lib/routing/wb-router-link.directive.ts
index 628647bb5..03b3734b8 100644
--- a/projects/scion/workbench/src/lib/routing/wb-router-link.directive.ts
+++ b/projects/scion/workbench/src/lib/routing/wb-router-link.directive.ts
@@ -78,7 +78,7 @@ export class WbRouterLinkDirective {
 export class WbRouterLinkWithHrefDirective extends WbRouterLinkDirective implements OnChanges {
 
   @HostBinding('href')
-  public href!: string;
+  public href: string | undefined;
 
   constructor(private _router: Router,
               private _locationStrategy: LocationStrategy,
diff --git a/projects/scion/workbench/src/lib/routing/workbench-auxiliary-routes-registrator.service.ts b/projects/scion/workbench/src/lib/routing/workbench-auxiliary-routes-registrator.service.ts
index 25346aaef..6e140ad61 100644
--- a/projects/scion/workbench/src/lib/routing/workbench-auxiliary-routes-registrator.service.ts
+++ b/projects/scion/workbench/src/lib/routing/workbench-auxiliary-routes-registrator.service.ts
@@ -42,7 +42,7 @@ export class WorkbenchAuxiliaryRoutesRegistrator {
       }));
 
     this.replaceRouterConfig([
-      ...this._router.config.filter(route => route.outlet === undefined || !outletNames.has(route.outlet)), // all registered routes, except auxiliary routes for any of the given outlets
+      ...this._router.config.filter(route => !route.outlet || !outletNames.has(route.outlet)), // all registered routes, except auxiliary routes for any of the given outlets
       ...outletAuxRoutes,
     ]);
 
@@ -58,7 +58,7 @@ export class WorkbenchAuxiliaryRoutesRegistrator {
       return;
     }
 
-    this.replaceRouterConfig(this._router.config.filter(route => route.outlet === undefined || !outletNames.has(route.outlet)));
+    this.replaceRouterConfig(this._router.config.filter(route => !route.outlet || !outletNames.has(route.outlet)));
   }
 
   /**
diff --git a/projects/scion/workbench/src/lib/routing/workbench-router.service.ts b/projects/scion/workbench/src/lib/routing/workbench-router.service.ts
index 4574fdbf4..7d2c8bdd0 100644
--- a/projects/scion/workbench/src/lib/routing/workbench-router.service.ts
+++ b/projects/scion/workbench/src/lib/routing/workbench-router.service.ts
@@ -55,7 +55,7 @@ export class WorkbenchRouter {
    *
    * @see WbRouterLinkDirective
    */
-  public async navigate(commandList: any[], extras: WbNavigationExtras = {}): Promise<boolean> {
+  public async navigate(commandList: Commands, extras: WbNavigationExtras = {}): Promise<boolean> {
     const commands = this.normalizeCommands(commandList, extras.relativeTo);
 
     if (extras.closeIfPresent) {
@@ -208,7 +208,7 @@ export class WorkbenchRouter {
    *
    * @internal
    */
-  public resolvePresentViewIds(commands: any[]): string[] {
+  public resolvePresentViewIds(commands: Commands): string[] {
     const serializeCommands = this.serializeCommands(commands);
     const urlTree = this._router.parseUrl(this._router.url);
     const urlSegmentGroups = urlTree.root.children;
@@ -378,7 +378,7 @@ export interface WorkbenchNavigationContext {
 }
 
 /**
- * An array of URL fragments with which to construct the target URL.
+ * An array of URL fragments with which to construct a view's URL.
  *
  * If the path is static, can be the literal URL string. For a dynamic path, pass an array of path segments,
  * followed by the parameters for each segment.
@@ -388,8 +388,6 @@ export interface WorkbenchNavigationContext {
  * available in {@link ActivatedRoute#params}.
  *
  * Example command array with 'details' as matrix parameter: `['user', userName, {details: true}]`,
- *
- * @internal
  */
 export type Commands = any[];
 
diff --git a/projects/scion/workbench/src/lib/routing/workbench-url-observer.service.ts b/projects/scion/workbench/src/lib/routing/workbench-url-observer.service.ts
index 08c627f87..565b05cbf 100644
--- a/projects/scion/workbench/src/lib/routing/workbench-url-observer.service.ts
+++ b/projects/scion/workbench/src/lib/routing/workbench-url-observer.service.ts
@@ -104,7 +104,7 @@ export class WorkbenchUrlObserver implements OnDestroy {
    */
   private computeWorkbenchLayoutDiff(url: string): WorkbenchNavigationContext {
     const urlTree = this._router.parseUrl(url);
-    const serializedPartsLayout = urlTree.queryParamMap.get(PARTS_LAYOUT_QUERY_PARAM)!;
+    const serializedPartsLayout = urlTree.queryParamMap.get(PARTS_LAYOUT_QUERY_PARAM) ?? undefined;
     const partsLayout = this._partsLayoutFactory.create(serializedPartsLayout);
     return {
       partsLayout,
@@ -144,9 +144,9 @@ export class WorkbenchUrlObserver implements OnDestroy {
    * Invoke this method after navigation failure or cancellation. The navigation is cancelled when guards perform a redirect or reject navigation.
    */
   private undoWorkbenchLayoutDiffer(): void {
-    const preNavigateUrl = this._router.url; // Browser URL is only updated after successful navigation
-    const preNavigateLayout = this._layoutService.layout!; // Layout in `LayoutService` is only updated after successful navigation
-    this._workbenchLayoutDiffer.diff(this._router.parseUrl(preNavigateUrl), preNavigateLayout);
+    const prevNavigateUrl = this._router.url; // Browser URL is only updated after successful navigation
+    const prevNavigateLayout = this._layoutService.layout; // Layout in `LayoutService` is only updated after successful navigation
+    this._workbenchLayoutDiffer.diff(this._router.parseUrl(prevNavigateUrl), prevNavigateLayout ?? undefined);
   }
 
   /**
@@ -277,7 +277,7 @@ export class WorkbenchUrlObserver implements OnDestroy {
     this._router.events
       .pipe(
         filter((event): event is RouterEvent => event instanceof RouterEvent),
-        takeUntil(this._destroy$)
+        takeUntil(this._destroy$),
       )
       .subscribe((event: RouterEvent) => {
         if (event instanceof NavigationStart) {
diff --git a/projects/scion/workbench/src/lib/sash.directive.ts b/projects/scion/workbench/src/lib/sash.directive.ts
index 7ddded90b..d19125764 100644
--- a/projects/scion/workbench/src/lib/sash.directive.ts
+++ b/projects/scion/workbench/src/lib/sash.directive.ts
@@ -22,7 +22,7 @@ import { first, takeUntil } from 'rxjs/operators';
 export class SashDirective implements OnDestroy, OnChanges {
 
   private _destroy$ = new Subject<void>();
-  private _mousePosition: number | null = null;
+  private _mousePosition: number | undefined;
 
   @Input('wbSash') // tslint:disable-line:no-input-rename
   public wbDirection: 'vertical' | 'horizontal' = 'horizontal';
@@ -40,7 +40,7 @@ export class SashDirective implements OnDestroy, OnChanges {
   public wbSashReset = new EventEmitter<void>(false);
 
   @HostBinding('style.cursor')
-  public cursor!: string;
+  public cursor: string | undefined;
 
   constructor(@Inject(DOCUMENT) private _document: any) {
   }
@@ -86,7 +86,7 @@ export class SashDirective implements OnDestroy, OnChanges {
       )
       .subscribe(() => {
         mousemoveListener.unsubscribe();
-        this._mousePosition = null;
+        this._mousePosition = undefined;
         this._document.body.style.cursor = oldCursor;
         this.wbSashEnd.next();
       });
diff --git a/projects/scion/workbench/src/lib/view-dnd/view-drag.service.ts b/projects/scion/workbench/src/lib/view-dnd/view-drag.service.ts
index b13bc28e7..2bec83d4e 100644
--- a/projects/scion/workbench/src/lib/view-dnd/view-drag.service.ts
+++ b/projects/scion/workbench/src/lib/view-dnd/view-drag.service.ts
@@ -49,7 +49,7 @@ export class ViewDragService {
   /**
    * Indicates if this app is the drag source for the ongoing drag operation (if any).
    */
-  private _isDragSource!: boolean;
+  private _isDragSource = false;
 
   constructor(private _broadcastChannel: BroadcastChannelService, private _zone: NgZone) {
     fromEvent(window, 'unload')
@@ -234,6 +234,7 @@ export interface ViewMoveEvent {
   target: {
     /**
      * Part to which to add the view. If using a {@link region} other than 'center', that part is used as a reference for creating a new part.
+     * Set the part to `null` if moving the view to a blank window.
      */
     partId: string | null;
     /**
diff --git a/projects/scion/workbench/src/lib/view-dnd/view-tab-drag-image-renderer.service.ts b/projects/scion/workbench/src/lib/view-dnd/view-tab-drag-image-renderer.service.ts
index 205bd5c8c..17984c12f 100644
--- a/projects/scion/workbench/src/lib/view-dnd/view-tab-drag-image-renderer.service.ts
+++ b/projects/scion/workbench/src/lib/view-dnd/view-tab-drag-image-renderer.service.ts
@@ -34,9 +34,9 @@ export type ConstrainFn = (rect: ViewDragImageRect) => ViewDragImageRect;
 export class ViewTabDragImageRenderer implements OnDestroy {
 
   private _destroy$ = new Subject<void>();
-  private _viewDragImagePortalOutlet!: DomPortalOutlet | null;
-  private _constrainDragImageRectFn!: ((rect: ViewDragImageRect) => ViewDragImageRect) | null;
-  private _dragData!: ViewDragData | null;
+  private _viewDragImagePortalOutlet: DomPortalOutlet | null = null;
+  private _constrainDragImageRectFn: ((rect: ViewDragImageRect) => ViewDragImageRect) | null = null;
+  private _dragData: ViewDragData | null = null;
 
   constructor(private _viewDragService: ViewDragService,
               private _workbenchModuleConfig: WorkbenchModuleConfig,
diff --git a/projects/scion/workbench/src/lib/view-part/view-context-menu/view-menu.service.ts b/projects/scion/workbench/src/lib/view-part/view-context-menu/view-menu.service.ts
index 37aff916a..347a2af83 100644
--- a/projects/scion/workbench/src/lib/view-part/view-context-menu/view-menu.service.ts
+++ b/projects/scion/workbench/src/lib/view-part/view-context-menu/view-menu.service.ts
@@ -18,7 +18,7 @@ import { filter, mapTo, switchMap, take, takeUntil, tap } from 'rxjs/operators';
 import { fromEvent, merge, Observable, Subject, TeardownLogic } from 'rxjs';
 import { coerceElement } from '@angular/cdk/coercion';
 import { TEXT, TextComponent } from '../view-context-menu/text.component';
-import { WorkbenchModuleConfig } from '../../workbench-module-config';
+import { MenuItemConfig, WorkbenchModuleConfig } from '../../workbench-module-config';
 import { WorkbenchService } from '../../workbench.service';
 import { Arrays } from '@scion/toolkit/util';
 import { filterArray } from '@scion/toolkit/operators';
@@ -135,8 +135,8 @@ export class ViewMenuService {
   }
 
   private registerCloseViewMenuItem(): void {
-    const defaults = {visible: true, text: 'Close tab', group: 'close', accelerator: ['ctrl', 'k']};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.close;
+    const defaults: MenuItemConfig = {visible: true, text: 'Close tab', group: 'close', accelerator: ['ctrl', 'k']};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.close;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -154,8 +154,8 @@ export class ViewMenuService {
   }
 
   private registerCloseOtherViewsMenuItem(): void {
-    const defaults = {visible: true, text: 'Close other tabs', group: 'close', accelerator: ['ctrl', 'shift', 'k']};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.closeOthers;
+    const defaults: MenuItemConfig = {visible: true, text: 'Close other tabs', group: 'close', accelerator: ['ctrl', 'shift', 'k']};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.closeOthers;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -174,8 +174,8 @@ export class ViewMenuService {
   }
 
   private registerCloseAllViewsMenuItem(): void {
-    const defaults = {visible: true, text: 'Close all tabs', group: 'close', accelerator: ['ctrl', 'shift', 'alt', 'k']};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.closeAll;
+    const defaults: MenuItemConfig = {visible: true, text: 'Close all tabs', group: 'close', accelerator: ['ctrl', 'shift', 'alt', 'k']};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.closeAll;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -193,8 +193,8 @@ export class ViewMenuService {
   }
 
   private registerCloseViewsToTheRightMenuItem(): void {
-    const defaults = {visible: true, text: 'Close tabs to the right', group: 'close', accelerator: undefined};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.closeToTheRight;
+    const defaults: MenuItemConfig = {visible: true, text: 'Close tabs to the right', group: 'close'};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.closeToTheRight;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -213,8 +213,8 @@ export class ViewMenuService {
   }
 
   private registerCloseViewsToTheLeftMenuItem(): void {
-    const defaults = {visible: true, text: 'Close tabs to the left', group: 'close', accelerator: undefined};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.closeToTheLeft;
+    const defaults: MenuItemConfig = {visible: true, text: 'Close tabs to the left', group: 'close'};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.closeToTheLeft;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -233,8 +233,8 @@ export class ViewMenuService {
   }
 
   private registerMoveRightMenuItem(): void {
-    const defaults = {visible: true, text: 'Move right', group: 'move', accelerator: ['ctrl', 'alt', 'end']};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.moveRight;
+    const defaults: MenuItemConfig = {visible: true, text: 'Move right', group: 'move', accelerator: ['ctrl', 'alt', 'end']};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.moveRight;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -253,8 +253,8 @@ export class ViewMenuService {
   }
 
   private registerMoveLeftMenuItem(): void {
-    const defaults = {visible: true, text: 'Move left', group: 'move', accelerator: undefined};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.moveLeft;
+    const defaults: MenuItemConfig = {visible: true, text: 'Move left', group: 'move'};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.moveLeft;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -273,8 +273,8 @@ export class ViewMenuService {
   }
 
   private registerMoveUpMenuItem(): void {
-    const defaults = {visible: true, text: 'Move up', group: 'move', accelerator: undefined};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.moveUp;
+    const defaults: MenuItemConfig = {visible: true, text: 'Move up', group: 'move'};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.moveUp;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -293,8 +293,8 @@ export class ViewMenuService {
   }
 
   private registerMoveDownMenuItem(): void {
-    const defaults = {visible: true, text: 'Move down', group: 'move', accelerator: undefined};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.moveDown;
+    const defaults: MenuItemConfig = {visible: true, text: 'Move down', group: 'move'};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.moveDown;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
@@ -313,8 +313,8 @@ export class ViewMenuService {
   }
 
   private registerMoveToNewWindowMenuItem(): void {
-    const defaults = {visible: true, text: 'Move to new window', group: 'open', accelerator: undefined};
-    const appConfig = this._workbenchModuleConfig.viewMenuItems?.moveBlank;
+    const defaults: MenuItemConfig = {visible: true, text: 'Move to new window', group: 'open'};
+    const appConfig: MenuItemConfig | undefined = this._workbenchModuleConfig.viewMenuItems?.moveBlank;
     const config = {...defaults, ...appConfig};
 
     config.visible && this._workbench.registerViewMenuItem((view: WorkbenchView): WorkbenchMenuItem => {
diff --git a/projects/scion/workbench/src/lib/view-part/view-tab-content/view-tab-content.component.ts b/projects/scion/workbench/src/lib/view-part/view-tab-content/view-tab-content.component.ts
index 2bbb9025a..64cf7740d 100644
--- a/projects/scion/workbench/src/lib/view-part/view-tab-content/view-tab-content.component.ts
+++ b/projects/scion/workbench/src/lib/view-part/view-tab-content/view-tab-content.component.ts
@@ -32,8 +32,8 @@ export class ViewTabContentComponent {
   }
 
   @HostBinding('class.blocked')
-  public get blocked(): boolean | null {
-    return this.view.blocked ?? null;
+  public get blocked(): boolean {
+    return this.view.blocked;
   }
 
   public onClose(event: Event): void {
diff --git a/projects/scion/workbench/src/lib/view-part/view-tab/view-tab.component.ts b/projects/scion/workbench/src/lib/view-part/view-tab/view-tab.component.ts
index 78864105a..74e6734d2 100644
--- a/projects/scion/workbench/src/lib/view-part/view-tab/view-tab.component.ts
+++ b/projects/scion/workbench/src/lib/view-part/view-tab/view-tab.component.ts
@@ -125,13 +125,15 @@ export class ViewTabComponent implements OnDestroy {
   @HostListener('dragstart', ['$event'])
   public onDragStart(event: DragEvent): void {
     this._viewPart.activateView(this.viewId).then(() => {
-      if (event.dataTransfer) {
-        event.dataTransfer.effectAllowed = 'move';
-        event.dataTransfer.setData(VIEW_DRAG_TRANSFER_TYPE, this.view.viewId);
-        // Use an invisible <div> as the native drag image because the effective drag image is rendered by {ViewTabDragImageRenderer}.
-        event.dataTransfer.setDragImage(createElement('div', {style: {display: 'none'}}), 0, 0);
+      if (!event.dataTransfer) {
+        return;
       }
 
+      event.dataTransfer.effectAllowed = 'move';
+      event.dataTransfer.setData(VIEW_DRAG_TRANSFER_TYPE, this.view.viewId);
+      // Use an invisible <div> as the native drag image because the effective drag image is rendered by {ViewTabDragImageRenderer}.
+      event.dataTransfer.setDragImage(createElement('div', {style: {display: 'none'}}), 0, 0);
+
       this._viewDragService.setViewDragData({
         viewId: this.view.viewId,
         viewTitle: this.view.title ?? '',
diff --git a/projects/scion/workbench/src/lib/view-part/workbench-view-part.registry.ts b/projects/scion/workbench/src/lib/view-part/workbench-view-part.registry.ts
index 2ac86cb91..191b8b9e3 100644
--- a/projects/scion/workbench/src/lib/view-part/workbench-view-part.registry.ts
+++ b/projects/scion/workbench/src/lib/view-part/workbench-view-part.registry.ts
@@ -27,10 +27,17 @@ export class WorkbenchViewPartRegistry implements OnDestroy {
    * Destroys the viewpart of the given id and removes it from this registry.
    */
   public remove(partId: string): void {
-    this._viewPartRegistry.get(partId)!.destroy();
+    this.getElseThrow(partId).destroy();
     this._viewPartRegistry.delete(partId);
   }
 
+  /**
+   * Returns the {@link WorkbenchViewPart} of the given identity, or `null` if not found.
+   */
+  public getElseNull(partId: string): ɵWorkbenchViewPart | null {
+    return this._viewPartRegistry.get(partId) || null;
+  }
+
   /**
    * Returns the {@link WorkbenchViewPart} of the given identity, or throws an Error if not found.
    */
diff --git "a/projects/scion/workbench/src/lib/view-part/\311\265workbench-view-part.model.ts" "b/projects/scion/workbench/src/lib/view-part/\311\265workbench-view-part.model.ts"
index c52d5d8e8..8e94e8939 100644
--- "a/projects/scion/workbench/src/lib/view-part/\311\265workbench-view-part.model.ts"
+++ "b/projects/scion/workbench/src/lib/view-part/\311\265workbench-view-part.model.ts"
@@ -45,15 +45,15 @@ export class ɵWorkbenchViewPart implements WorkbenchViewPart { // tslint:disabl
 
     this._part = part;
     viewIdsChange && this.viewIds$.next(part.viewIds);
-    activeViewChange && this.activeViewId$.next(part.activeViewId!);
+    activeViewChange && this.activeViewId$.next(part.activeViewId ?? null);
   }
 
   public get viewIds(): string[] {
     return this._part.viewIds;
   }
 
-  public get activeViewId(): string {
-    return this._part.activeViewId!;
+  public get activeViewId(): string | null {
+    return this._part.activeViewId ?? null;
   }
 
   public registerViewPartAction(action: WorkbenchViewPartAction): Disposable {
@@ -109,11 +109,11 @@ export class ɵWorkbenchViewPart implements WorkbenchViewPart { // tslint:disabl
    * Note: This instruction runs asynchronously via URL routing.
    */
   public async activateSiblingView(): Promise<boolean> {
-    if (this._markedForDestruction) {
+    if (this._markedForDestruction || !this.activeViewId) {
       return false;
     }
 
-    return this._wbRouter.ɵnavigate(layout => layout.activateAdjacentView(this.activeViewId));
+    return this._wbRouter.ɵnavigate(layout => layout.activateAdjacentView(this.activeViewId!));
   }
 
   public isActive(): boolean {
diff --git a/projects/scion/workbench/src/lib/view/view-move-handler.service.ts b/projects/scion/workbench/src/lib/view/view-move-handler.service.ts
index 2188cf42f..4edcbf16e 100644
--- a/projects/scion/workbench/src/lib/view/view-move-handler.service.ts
+++ b/projects/scion/workbench/src/lib/view/view-move-handler.service.ts
@@ -72,7 +72,8 @@ export class ViewMoveHandler implements OnDestroy {
   }
 
   private addView(event: ViewMoveEvent): void {
-    const addToNewViewPart = (event.target.region || 'center') !== 'center';
+    const region = event.target.region || 'center';
+    const addToNewViewPart = region !== 'center';
 
     const commands = RouterUtils.segmentsToCommands(event.source.viewUrlSegments);
     if (addToNewViewPart) {
@@ -80,7 +81,7 @@ export class ViewMoveHandler implements OnDestroy {
       const newPartId = event.target.newPartId || UUID.randomUUID();
       this._wbRouter.ɵnavigate(layout => ({
         layout: layout
-          .addPart(newPartId, {relativeTo: event.target.partId!, align: coerceLayoutAlignment(event.target.region!)})
+          .addPart(newPartId, {relativeTo: event.target.partId ?? undefined, align: coerceLayoutAlignment(region)})
           .addView(newPartId, newViewId),
         viewOutlets: {[newViewId]: commands},
       })).then();
diff --git a/projects/scion/workbench/src/lib/view/view-portal.pipe.ts b/projects/scion/workbench/src/lib/view/view-portal.pipe.ts
index 75329f51e..d04525510 100644
--- a/projects/scion/workbench/src/lib/view/view-portal.pipe.ts
+++ b/projects/scion/workbench/src/lib/view/view-portal.pipe.ts
@@ -23,6 +23,9 @@ export class ViewPortalPipe implements PipeTransform {
   }
 
   public transform<T>(viewId: string | null): WbComponentPortal<ViewComponent> | null {
-    return viewId ? this._viewRegistry.get(viewId)?.portal ?? null : null;
+    if (!viewId) {
+      return null;
+    }
+    return this._viewRegistry.getElseNull(viewId)?.portal ?? null;
   }
 }
diff --git a/projects/scion/workbench/src/lib/view/workbench-view.model.ts b/projects/scion/workbench/src/lib/view/workbench-view.model.ts
index a3e00e57c..34d065d64 100644
--- a/projects/scion/workbench/src/lib/view/workbench-view.model.ts
+++ b/projects/scion/workbench/src/lib/view/workbench-view.model.ts
@@ -51,7 +51,7 @@ export abstract class WorkbenchView {
   /**
    * Specifies if the view is blocked, e.g., not interactable because of showing a view-modal message box.
    */
-  public abstract blocked?: boolean;
+  public abstract blocked: boolean;
 
   /**
    * Specifies if a close button should be displayed in the view tab.
diff --git a/projects/scion/workbench/src/lib/view/workbench-view.registry.ts b/projects/scion/workbench/src/lib/view/workbench-view.registry.ts
index 95d7bf21d..b0dafe23d 100644
--- a/projects/scion/workbench/src/lib/view/workbench-view.registry.ts
+++ b/projects/scion/workbench/src/lib/view/workbench-view.registry.ts
@@ -32,7 +32,7 @@ export class WorkbenchViewRegistry implements OnDestroy {
    * Destroys the view of the given id and removes it from this registry.
    */
   public remove(viewId: string): void {
-    this._viewRegistry.get(viewId)!.destroy();
+    this.getElseThrow(viewId).destroy();
     this._viewRegistry.delete(viewId);
     this._viewRegistryChange$.next();
   }
@@ -65,10 +65,10 @@ export class WorkbenchViewRegistry implements OnDestroy {
   }
 
   /**
-   * Returns the {@link WorkbenchView} of the given identity, or returns `undefined` if not found.
+   * Returns the {@link WorkbenchView} of the given identity, or returns `null` if not found.
    */
-  public get(viewId: string): ɵWorkbenchView | undefined {
-    return this._viewRegistry.get(viewId);
+  public getElseNull(viewId: string): ɵWorkbenchView | null {
+    return this._viewRegistry.get(viewId) ?? null;
   }
 
   public get viewIds(): string[] {
diff --git a/projects/scion/workbench/src/lib/workbench.service.ts b/projects/scion/workbench/src/lib/workbench.service.ts
index 6d81ef32a..35bc9f591 100644
--- a/projects/scion/workbench/src/lib/workbench.service.ts
+++ b/projects/scion/workbench/src/lib/workbench.service.ts
@@ -37,7 +37,7 @@ export abstract class WorkbenchService {
   /**
    * A unique ID per instance of the app. If opened in a different browser tab, it has a different instance ID.
    */
-  public readonly appInstanceId!: string;
+  public abstract readonly appInstanceId: string;
 
   /**
    * Emits the views opened in the workbench.
@@ -45,7 +45,7 @@ export abstract class WorkbenchService {
    * Upon subscription, the currently opened views are emitted, and then emits continuously
    * when new views are opened or existing views closed. It never completes.
    */
-  public readonly views$!: Observable<string[]>;
+  public abstract readonly views$: Observable<string[]>;
 
   /**
    * Returns a reference to the specified {@link WorkbenchView}, or `null` if not found.
diff --git "a/projects/scion/workbench/src/lib/\311\265workbench.service.ts" "b/projects/scion/workbench/src/lib/\311\265workbench.service.ts"
index 4adf7b88e..7490a8c30 100644
--- "a/projects/scion/workbench/src/lib/\311\265workbench.service.ts"
+++ "b/projects/scion/workbench/src/lib/\311\265workbench.service.ts"
@@ -9,7 +9,7 @@
  */
 
 import { Injectable } from '@angular/core';
-import { BehaviorSubject, Observable } from 'rxjs';
+import { BehaviorSubject } from 'rxjs';
 import { WorkbenchMenuItemFactoryFn, WorkbenchViewPartAction } from './workbench.model';
 import { UUID } from '@scion/toolkit/uuid';
 import { WorkbenchLayoutService } from './layout/workbench-layout.service';
@@ -25,6 +25,7 @@ export class ɵWorkbenchService implements WorkbenchService { // tslint:disable-
 
   public readonly viewPartActions$ = new BehaviorSubject<WorkbenchViewPartAction[]>([]);
   public readonly viewMenuItemProviders$ = new BehaviorSubject<WorkbenchMenuItemFactoryFn[]>([]);
+  public readonly views$ = this._layoutService.layout$.pipe(map(layout => layout.parts.reduce((viewIds, part) => viewIds.concat(part.viewIds), new Array<string>())));
   public readonly appInstanceId = UUID.randomUUID();
 
   constructor(private _wbRouter: WorkbenchRouter,
@@ -44,12 +45,8 @@ export class ɵWorkbenchService implements WorkbenchService { // tslint:disable-
     return this._layoutService.layout!.findPartByViewId(viewId, {orElseThrow: true}).partId;
   }
 
-  public get views$(): Observable<string[]> {
-    return this._layoutService.layout$.pipe(map(layout => layout.parts.reduce((viewIds, part) => viewIds.concat(part.viewIds), new Array<string>())));
-  }
-
   public getView(viewId: string): WorkbenchView | null {
-    return this._viewRegistry.get(viewId) ?? null;
+    return this._viewRegistry.getElseNull(viewId);
   }
 
   public registerViewPartAction(action: WorkbenchViewPartAction): Disposable {