public Mono<Boolean> isBlocked(@NotNull Long groupId, @NotNull Long userId) {
        try {
            Validator.notNull(groupId, "groupId");
            Validator.notNull(userId, "userId");
        } catch (ResponseException e) {
            return Mono.error(e);
        }
        GroupBlockedUser.Key key = new GroupBlockedUser.Key(groupId, userId);
        return groupBlocklistRepository.existsById(key);
    }
@return whether the user to unblock was blocked
turms-service/src/main/java/im/turms/service/domain/group/service/GroupBlocklistService.java