[BUGFIX] Prevent fatal error in DebugExceptionHandler

This patch fixes an error if no argument was given for a trace step.

Resolves: #86211
Releases: master
Change-Id: Iee26940df2c463fc0badde245f9da92e73f6740e
Reviewed-on: https://review.typo3.org/58242


Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>

typo3/sysext/core/Classes/Error/DebugExceptionHandler.php

@@ -394,7 +394,7 @@ STYLESHEET;
 
         foreach ($trace as $index => $step) {
             $content .= '<div class="trace-step">';
-            $args = $this->flattenArgs($step['args']);
+            $args = $this->flattenArgs($step['args'] ?? []);
 
             if (isset($step['function'])) {
                 $content .= '<div class="trace-call">' . sprintf(