public Mono<Set<Long>> queryMeetingParticipants(@Nullable Long userId, @Nullable Long groupId) {
        if (userId != null) {
            return Mono.just(Set.of(userId));
        }
        if (groupId != null) {
            return groupMemberService.queryGroupMemberIds(groupId, false);
        }
        return PublisherPool.emptySet();
    }
Use {@link SecureRandom} because users usually input meeting IDs to join meetings, so we
should make sure they are unpredictable.
turms-service/src/main/java/im/turms/service/domain/conference/service/ConferenceService.java