htmlspecialchars() - Deprecation warning in php 8.1

[MaximilianKresse]

Code:

$smarty = new \Smarty();
$smarty->setEscapeHtml(true);

$smarty->assign('value', null);

var_dump($smarty->fetch('string:{$value}'));

Expected output:

string(0) ""

Output in php >= 8.1:

string(215) "
Deprecated: htmlspecialchars(): Passing null to parameter #1 ($string) of type string is deprecated in ...\7f3eb64ac896f10d0f0414cf415a097993be285b_2.string.php on line 18
"

I could fix this problem with a "default"-modifier but I think smarty should be robust enough to prevent this kind of errors. I see the problem in this line here.
The {$output} should be casted to string to prevent this error.

[wisskid]

Thanks @MaximilianKresse. Closing this in favor of #750