public function addMember($member)
    {
        $member = ($member instanceof Model ? $member->getDn() : $member);

        if (is_null($member)) {
            throw new InvalidArgumentException(
                'Cannot add member to group. The members distinguished name cannot be null.'
            );
        }

        $mod = $this->newBatchModification(
            $this->schema->member(),
            LDAP_MODIFY_BATCH_ADD,
            [$member]
        );

        return $this->addModification($mod)->save();
    }