Give an option for null studies

src/app/settings.service.ts

@@ -10,7 +10,11 @@ export class SettingsService {
   constructor() { }
 
   setStudyIdForValidation(id: number) {
-    localStorage.setItem(this.studyIdKey, id.toString());
+    if (id != null) {
+      localStorage.setItem(this.studyIdKey, id.toString());
+    } else {
+      localStorage.removeItem(this.studyIdKey)
+    }
   }
 
   getStudyIdForValidation() {

src/app/settings/settings.component.html

@@ -6,6 +6,7 @@
     <mat-label>Select Study</mat-label>
     <mat-hint>Here you can specify a default study to use when performing validation.</mat-hint>
     <mat-select matNativeControl required [(value)]="selectedStudyId" (selectionChange)="selectStudy($event.value)">
+      <mat-option [value]="null"> No study selected </mat-option>
       <mat-option *ngFor="let s of studies" [value]="s.id">
         {{s.id}} - {{s.title}}
       </mat-option>