diff -urN ../z-push-2.6.2+0.orig/src/include/mimeDecode.php ./src/include/mimeDecode.php
--- ../z-push-2.6.2+0.orig/src/include/mimeDecode.php	2023-03-18 01:57:07.838734000 +0200
+++ ./src/include/mimeDecode.php	2023-03-18 01:57:52.512261000 +0200
@@ -874,7 +874,7 @@
                 break;
         }
 
-        if ($detectCharset && strtolower($charset) != $this->_charset) {
+        if ($detectCharset && $charset && strtolower($charset) != $this->_charset) {
             if (@mb_check_encoding($input, $charset) == false) {
                 // list of encodings, sorted by priority to assist mb_detect_encoding()
                 $encodingPriority = array('UTF-8', 'SJIS', 'GB18030', 'ISO-8859-1', 'ISO-8859-2', 'ISO-8859-3', 'ISO-8859-4',