public UserDto translateUsernameToUserDto(String username) {
        return Optional.ofNullable(tryAction(() -> storage.getUser(username)))
                       .map(userMapper::toDto)
                       .orElse(new UserDto().setUsername("external-or-deleted-user"));
    }
@author Marc Savy {@literal <marc@blackparrotlabs.io>}
manager/api/rest-impl/src/main/java/io/apiman/manager/api/notifications/mappers/NotificationMapper.java