fix: correct to avoid NPE + add missing message

refactor code to avoid NPE + add missing message.

DLCM-Admin/src/main/java/ch/dlcm/business/NotificationService.java

@@ -240,7 +240,8 @@ public class NotificationService extends ResourceService<Notification> {
         SolidifyEventPublisher.getPublisher().publishEvent(Objects.requireNonNull(emailMessage));
       }
     }
-    if (item.getNotificationType().getNotificationCategory().equals(NotificationCategory.INFO)) {
+    if (item.getNotificationType().getNotificationCategory() != null && item.getNotificationType().getNotificationCategory()
+            .equals(NotificationCategory.INFO)) {
       item.setNotificationStatus(NotificationStatus.NON_APPLICABLE);
     }
     return super.save(item);