Description:
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string cast dont work with zero values.

Test script:
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// test.php?price=0
$price = $_GET['price'];
echo htmlspecialchars((string)$price, ENT_QUOTES); // empty
// cast (string) for prevent errors with arrays, for example test.php?price[][][][]=disclosureHere

Expected result:
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0 not empty

Patch in php:
// test.php?price=0
$price = $_GET['price'];
echo (($price === '0') ? '0' : htmlspecialchars((string)$price, ENT_QUOTES));

Actual result:
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empty value :-/