OZG-4949 Use explicit `FormControl`

alfa-client/libs/admin-settings/src/lib/postfach/postfach-container/postfach-form/postfach.formservice.spec.ts

@@ -44,7 +44,7 @@ describe('PostfachFormService', () => {
       expect(postfachService.save).toHaveBeenCalledWith(postfach);
     });
 
-    describe('without absender values', () => {
+    describe('with empty or null absender values', () => {
       const formValueWithAbsender = {
         [PostfachFormService.ASBSENDER_GROUP]: {
           [PostfachFormService.NAME_FIELD]: '',

alfa-client/libs/admin-settings/src/lib/postfach/postfach-container/postfach-form/postfach.formservice.ts

 import { AbstractFormService, HttpError, StateResource } from '@alfa-client/tech-shared';
 import { Injectable } from '@angular/core';
-import { UntypedFormBuilder, UntypedFormGroup } from '@angular/forms';
+import { FormControl, UntypedFormBuilder, UntypedFormGroup } from '@angular/forms';
 import { Observable } from 'rxjs';
 import { PostfachService } from '../../postfach.service';
 import { Postfach, PostfachResource } from '../../postfach.model';
@@ -27,13 +27,13 @@ export class PostfachFormService extends AbstractFormService {
   protected initForm(): UntypedFormGroup {
     return this.formBuilder.group({
       [PostfachFormService.ASBSENDER_GROUP]: this.formBuilder.group({
-        [PostfachFormService.NAME_FIELD]: [''],
-        [PostfachFormService.ANSCHRIFT_FIELD]: [''],
-        [PostfachFormService.DIENST_FIELD]: [''],
-        [PostfachFormService.MANDANT_FIELD]: [''],
-        [PostfachFormService.GEMEINDESCHLUESSEL_FIELD]: [''],
+        [PostfachFormService.NAME_FIELD]: new FormControl(''),
+        [PostfachFormService.ANSCHRIFT_FIELD]: new FormControl(''),
+        [PostfachFormService.DIENST_FIELD]: new FormControl(''),
+        [PostfachFormService.MANDANT_FIELD]: new FormControl(''),
+        [PostfachFormService.GEMEINDESCHLUESSEL_FIELD]: new FormControl(''),
       }),
-      [PostfachFormService.SIGNATUR_FIELD]: [''],
+      [PostfachFormService.SIGNATUR_FIELD]: new FormControl(''),
     });
   }