ldap_search not working with base=NULL after php7.1

Description

The following code:

<?php
$ds = ldap_connect(); // <-- URI from /etc/openldap/ldap.conf
ldap_set_option($ds, LDAP_OPT_PROTOCOL_VERSION, 3);

$sr = ldap_search($ds, NULL, "(uid=dab)", array("dn"));  // <-- BASE from /etc/openldap/ldap.conf
$entry = ldap_first_entry($ds, $sr);
var_dump($entry);

Resulted in this output:

Warning: ldap_search(): Search: No such object in test.php on line 5

But I expected this output instead:

resource(6) of type (ldap result entry)

/etc/openldap/ldap.conf:
BASE c=ru
URI ldap://localhost

slapd.log:
version <=php7.1
slapd[14091]: conn=4230904 op=0 SRCH base="c=ru" scope=2 deref=0 filter="(uid=dab)"
version >php7.1
slapd[14091]: conn=4230791 op=0 SRCH base="" scope=2 deref=0 filter="(uid=dab)"

related bug&commit:
https://bugs.php.net/bug.php?id=77958
https://github.com/php/php-src/commit/5d2fe48785b6d24102ff53e78631cba7f2aefbef

PHP Version

PHP 8.0.12

Operating System

gentoo

Start at the ldap_search entry point and compare the behavior shown in the reproduction with the linked bug and commit 5d2fe48785b6d24102ff53e78631cba7f2aefbef. Run the provided PHP script against the stated LDAP configuration and inspect slapd.log; done means a NULL base uses the configured BASE and the search returns the expected entry.