Super Cache: Fix deprecation notices

[haqadn]

Fixes #32336

Proposed changes:

• Ensure $wp_cache_request_uri is always set to a string.

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Testing instructions:

None

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Super Cache plugin:

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[donnchawp]

I confirmed that $_SERVER['REQUEST_URI'] is NULL in a script run from the command line, so that is likely where the null value is coming from.

I saw in get_wp_cache_key in wp-cache-phase2.php (around line 40) that we fixed the same problem by checking for null. I think we can probably remove that check now with this fix.

[donnchawp]

Looks great. I checked where $wp_cache_request_uri is used and it's good.

[donnchawp]

deb8585

[A-Printer]

@donnchawp The removal of the if ( null === $url ) check causes a Deprecated notice to be thrown on the frontend when logged as an admin:

Also, the Deprecated notice causes the REST API check to fail on the Site Health page:

[donnchawp]

Fixed in #32629