Conform more code to strict null checking (#10167)

* Conform more code to strict null checking

* Delint

* Iterate PR based on feedback

src/stores/widgets/StopGapWidget.ts

@@ -216,8 +216,8 @@ export class StopGapWidget extends EventEmitter {
         const defaults: ITemplateParams = {
             widgetRoomId: this.roomId,
             currentUserId: this.client.getUserId()!,
-            userDisplayName: OwnProfileStore.instance.displayName,
-            userHttpAvatarUrl: OwnProfileStore.instance.getHttpAvatarUrl(),
+            userDisplayName: OwnProfileStore.instance.displayName ?? undefined,
+            userHttpAvatarUrl: OwnProfileStore.instance.getHttpAvatarUrl() ?? undefined,
             clientId: ELEMENT_CLIENT_ID,
             clientTheme: SettingsStore.getValue("theme"),
             clientLanguage: getUserLanguage(),

src/stores/widgets/WidgetLayoutStore.ts

@@ -477,7 +477,7 @@ export class WidgetLayoutStore extends ReadyWatchingStore {
         this.updateUserLayout(room, newLayout);
     }
 
-    public hasMaximisedWidget(room: Room): boolean {
+    public hasMaximisedWidget(room?: Room): boolean {
         return this.getContainerWidgets(room, Container.Center).length > 0;
     }