diff -urN ../roundcubemail-1.6.1.orig/program/lib/Roundcube/rcube_ldap.php ./program/lib/Roundcube/rcube_ldap.php
--- ../roundcubemail-1.6.1.orig/program/lib/Roundcube/rcube_ldap.php	2023-01-23 22:03:14.000000000 +0200
+++ ./program/lib/Roundcube/rcube_ldap.php	2023-03-15 23:04:18.701117000 +0200
@@ -187,7 +187,7 @@
                     (array) ($this->coltypes['address']['subtypes'] ?? null),
                     (array) ($this->coltypes['locality']['subtypes'] ?? null)
                 ),
-            ] + (array) $this->coltypes['address'];
+            ] + (isset($this->coltypes['address']) ? (array) $this->coltypes['address'] : []);
 
             foreach (['street','locality','zipcode','region','country'] as $childcol) {
                 if (!empty($this->coltypes[$childcol])) {
@@ -803,6 +803,12 @@
      */
     function _entry_sort_cmp($a, $b)
     {
+        if ((!isset($a[$this->sort_col][0])) or ($a[$this->sort_col][0] === null)) {
+            return(((!isset($b[$this->sort_col][0])) or ($b[$this->sort_col][0] === null)) ? 0 : -1);
+        }
+        if ((!isset($b[$this->sort_col][0])) or ($b[$this->sort_col][0] === null)) {
+            return(((!isset($a[$this->sort_col][0])) or ($a[$this->sort_col][0] === null)) ? 0 : 1);
+        }
         return strcmp($a[$this->sort_col][0], $b[$this->sort_col][0]);
     }