add link validation for an achievement

Author: Mutugiii

src/app/users/users-achievements/users-achievements-update.component.ts

@@ -133,7 +133,7 @@ export class UsersAchievementsUpdateComponent implements OnInit, OnDestroy {
         ...achievement,
         title: [ achievement.title, CustomValidators.required ],
         description: [ achievement.description ],
-        link: [ achievement.link ],
+        link: [ achievement.link, [], CustomValidators.validLink ],
         date: [ achievement.date, null, ac => this.validatorService.notDateInFuture$(ac) ]
       }),
       { onSubmit: (formValue, formGroup) => {

src/app/validators/custom-validators.ts

@@ -246,11 +246,15 @@ export class CustomValidators {
 
   static validLink(ac: AbstractControl): Promise<ValidationErrors | null> | Observable<ValidationErrors | null> {
     return new Promise((resolve, reject) => {
-      try {
-        const url = new URL(ac.value);
+      if (!ac.value) {
         resolve(null);
-      } catch (_) {
-        resolve({ 'invalidLink': true });
+      } else {
+        try {
+          const url = new URL(ac.value);
+          resolve(null);
+        } catch (_) {
+          resolve({ 'invalidLink': true });
+        }
       }
     });
   }