diff -urN ../roundcubemail-1.6.1.orig/program/lib/Roundcube/rcube_mime.php ./program/lib/Roundcube/rcube_mime.php
--- ../roundcubemail-1.6.1.orig/program/lib/Roundcube/rcube_mime.php	2023-01-23 22:03:14.000000000 +0200
+++ ./program/lib/Roundcube/rcube_mime.php	2023-04-12 11:43:12.668699000 +0300
@@ -484,7 +484,8 @@
      */
     public static function unfold_flowed($text, $mark = null, $delsp = false)
     {
-        $text    = preg_split('/\r?\n/', $text);
+//        $text    = preg_split('/\r?\n/', $text);
+        $text    = ( !empty($text) ? preg_split('/\r?\n/', $text) : [] );
         $last    = -1;
         $q_level = 0;
         $marks   = [];