hellofromTonya 847b7d8690 Code Modernization: Fix "passing null to non-nullable" deprecation in _mb_substr(). ...

The `_mb_substr()` function expects a string for the `$str` parameter, but does not do input validation. This function contains a `preg_match_all()` which also expects a string type for the given subject (i.e. `$str`). 

Passing `null` to this parameter results in `preg_match_all(): Passing null to parameter #2 ($subject) of type string is deprecated` notice on PHP 8.1.

To maintain the same behaviour as before, a guard clause is added to bail out early when `$str` is passed as `null`. The outcome will, in that case, only ever be an empty string.

Note: this does mean that the `_mb_substr()` function now has a subtle difference in behaviour compared to the PHP native `mb_substr()` function as the latter ''will'' throw the deprecation notice.

The existing tests already cover this issue.

Follow-up to [17621], [36017], [32364].

Props jrf, hellofromTonya.
See #53635.
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git-svn-id: http://core.svn.wordpress.org/trunk@51452 1a063a9b-81f0-0310-95a4-ce76da25c4cd

2021-09-22 23:34:57 +00:00

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