Use zero instead of null as empty arg for header() for PHP 8.1+ compat

[westonruter]

See #7225 (comment)

See also docs for header(): https://www.php.net/manual/en/function.header.php

The $response_code parameter is define as follows:

Forces the HTTP response code to the specified value. Note that this parameter only has an effect if the header is not empty.

Note empty here. So 0 and null should work the same since they are both empty.

Note also the function signature:

header(string $header, bool $replace = true, int $response_code = 0): void

The default value of $response_code is 0.

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[thelovekesh]

LGTM 🎉

[pavanpatil1]

QA Passed ✅

Tested it with PHP v8.1 and 8.2, Deprecation warning is not visible now.