From c2c6ca2cdb7cb7c08a1e96f39525525daf9cf0f8 Mon Sep 17 00:00:00 2001
From: Roland Eigelsreiter <brainfoolong@users.noreply.github.com>
Date: Wed, 8 Sep 2021 11:11:38 +0200
Subject: [PATCH] fixed null conversation for strToUpper

fixed in the same way as it already has been done for strToLower
---
 src/PhpSpreadsheet/Shared/StringHelper.php | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/PhpSpreadsheet/Shared/StringHelper.php b/src/PhpSpreadsheet/Shared/StringHelper.php
index 0e8eb8a5f3..a9e244070a 100644
--- a/src/PhpSpreadsheet/Shared/StringHelper.php
+++ b/src/PhpSpreadsheet/Shared/StringHelper.php
@@ -490,7 +490,7 @@ public static function substring($pValue, $pStart, $pLength = 0)
      */
     public static function strToUpper($pValue)
     {
-        return mb_convert_case($pValue, MB_CASE_UPPER, 'UTF-8');
+        return mb_convert_case($pValue ?? '', MB_CASE_UPPER, 'UTF-8');
     }
 
     /**