diff -urN ../roundcubemail-1.6.1.orig/vendor/kolab/net_ldap3/lib/Net/LDAP3.php ./vendor/kolab/net_ldap3/lib/Net/LDAP3.php
--- ../roundcubemail-1.6.1.orig/vendor/kolab/net_ldap3/lib/Net/LDAP3.php	2021-11-11 11:02:56.000000000 +0200
+++ ./vendor/kolab/net_ldap3/lib/Net/LDAP3.php	2023-03-16 15:16:57.267825000 +0200
@@ -2076,7 +2076,7 @@
     protected function find_vlv_indexes_and_searches()
     {
         // Use of Virtual List View control has been specifically disabled.
-        if ($this->config['vlv'] === false) {
+        if ((isset($this->config['vlv'])) and ($this->config['vlv'] === false)) {
             return false;
         }
 
@@ -2111,7 +2111,7 @@
         //             },
         //     ]
         //
-        if (is_array($this->config['vlv'])) {
+        if ((isset($this->config['vlv'])) and (is_array($this->config['vlv']))) {
             return $this->config['vlv'];
         }