|strip_tags:true filter does not work if the input is exactly the number 0

[ghost]

Reproduction:

$x=0;
{$x|strip_tags}

Expected:
0
Result:
Empty string

The Problem was introduced in https://github.com/smarty-php/smarty/blob/master/libs/plugins/modifiercompiler.strip_tags.php when a deprecation error was fixed here 612bd3f

The operator ? is a soft == instead of ?? which checks for hard empty.

Solution:
Check for 0 or use "??", but this would similar to #882

Alterantive Solution:
Check if the string even contains a "<" and then just return it, if not, then you save the whole regex.

Additional: The documenation on the true/false parameter is very unclear https://www.smarty.net/docs/en/language.modifier.strip.tags.tpl as it is hard to visualize the space when a linebreak is in the documentation, adding a sentence explaining the space or no space paradigma would help a lot.

[scottchiefbaker]

That code isn't easily readable. Couldn't you simplify the entire thing with something like:

$x = $params[1];
if (!is_string($x)) {
    return $x;
} else {
    return strip_tags($x);
}