Remove undefined value from checkbox

Can only be true/false.

projects/common/unit.ts

@@ -94,7 +94,7 @@ export interface TextAreaElement extends InputUIElement, TextUIElement, SurfaceU
 }
 
 export interface CheckboxElement extends InputUIElement, TextUIElement, SurfaceUIElement {
-  value: boolean | undefined;
+  value: boolean;
 }
 
 export interface DropdownElement extends InputUIElement, TextUIElement, SurfaceUIElement {

projects/editor/src/app/UnitFactory.ts

@@ -134,7 +134,7 @@ export function createTextareaElement(): TextAreaElement {
 export function createCheckboxElement(): CheckboxElement {
   return <CheckboxElement>{
     ...createUnitUIElement('checkbox'),
-    ...createInputUIElement('Label Checkbox', undefined),
+    ...createInputUIElement('Label Checkbox', false),
     ...createTextUIElement(),
     ...createSurfaceUIElement(),
     backgroundColor: 'transparent'

projects/editor/src/app/components/unit-view/page-view/properties/element-properties.component.ts

@@ -45,10 +45,10 @@ import { SelectionService } from '../../../../selection.service';
             </mat-form-field>
             <section *ngIf="combinedProperties.type === 'checkbox'">
               Vorbelegung
-              <mat-button-toggle-group (change)="transformToBoolAndUpdateModel('value', $event.value)">
-                <mat-button-toggle value="true">wahr</mat-button-toggle>
-                <mat-button-toggle value="false">falsch</mat-button-toggle>
-                <mat-button-toggle value="undefined">undefiniert</mat-button-toggle>
+              <mat-button-toggle-group [value]="combinedProperties.value"
+                                       (change)="updateModel('value', $event.value)">
+                <mat-button-toggle [value]="true">wahr</mat-button-toggle>
+                <mat-button-toggle [value]="false">falsch</mat-button-toggle>
               </mat-button-toggle-group>
             </section>
             <mat-form-field *ngIf="combinedProperties.type === 'dropdown' || combinedProperties.type === 'radio'"
@@ -399,24 +399,6 @@ export class ElementPropertiesComponent implements OnInit, OnDestroy {
     this.unitService.alignElements(this.selectionService.getSelectedElements(), direction);
   }
 
-  /* button group always handles values as string and since we also want to handle undefined
-   we need to transform the value before passing it on. */
-  transformToBoolAndUpdateModel(property: string, value: string): void { // TODO weg refactorn
-    switch (value) {
-      case 'true': {
-        this.updateModel(property, true);
-        break;
-      }
-      case 'false': {
-        this.updateModel(property, false);
-        break;
-      }
-      default: {
-        this.updateModel(property, undefined);
-      }
-    }
-  }
-
   deleteElement(): void {
     this.selectionService.selectedPageSection
       .pipe(take(1))