public Mono<DeleteResult> deleteRelationshipGroups(
            @NotEmpty Set<UserRelationshipGroup.@ValidUserRelationshipGroupKey Key> keys) {
        try {
            Validator.notEmpty(keys, "keys");
            for (UserRelationshipGroup.Key key : keys) {
                DataValidator.validRelationshipGroupKey(key);
            }
        } catch (ResponseException e) {
            return Mono.error(e);
        }
        return userRelationshipGroupRepository.deleteByIds(keys);
    }
@return true if added a new related user to the relationship group.
@implNote We call this method while upserting a relationship into the owner's relationship
          group in a transaction currently, so we don't check whether the owner has a
          relationship with the related user in this method.
turms-service/src/main/java/im/turms/service/domain/user/service/UserRelationshipGroupService.java