Theme JSON CSS var preset resolution: check for null values

[ramonopoly]

When using wp_get_global_styles() with the resolve-variables flag like this —

wp_get_global_styles( array( 'typography', 'fontSize' ), array( 'block_name' => 'core/search', 'transforms' => array( 'resolve-variables' ) ) );

It's possible to trigger the following error:

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Deprecated: strpos(): Passing null to parameter 1 ($haystack) of type string is deprecated in

Deprecated: preg_match_all(): Passing null to parameter 2 ($subject) of type string is deprecated

---

The complaint is about passing a null value to strpos() and preg_match_all() in WP_Theme_JSON::convert_variables_to_value

wp_get_global_styles attempt to resolve variables using merged data from WP_Theme_JSON_Resolver.

WP_Theme_JSON_Resolver::get_block_data() sets blockGap for supported blocks to null if the value is not defined.

Because WP_Theme_JSON_Gutenberg::convert_variables_to_value is expecting strings as values, it will trigger the error in this case.

Gutenberg PR: ​Theme JSON: Check for null values to cater for blockGap

Syncs changes from

• ​https://github.com/WordPress/gutenberg/pull/59258

When resolving theme.json preset variables, add a check to make sure the value is not empty before we run it through strpos() and preg_match_all().

Run the tests:

npm run test:php -- --filter Tests_Theme_wpThemeJson

Trac ticket: https://core.trac.wordpress.org/ticket/60613

[ramonopoly]

I added 6.5 to this ticket - hopefully it's not controversial.

Fine to be punted to 6.6.

@youknowriad I think this one is ready once ​the nits are addressed.

[youknowriad]

In 57716:

Editor: Check for null values in Theme JSON to cater for blockGap.

When resolving theme.json preset variables, add a check to make sure the value is not empty before we run it through strpos() and preg_match_all().

Props ramonopoly, mukesh27, get_dave.
Fixes #60613.

https://core.trac.wordpress.org/changeset/57716

Commit https://core.trac.wordpress.org/changeset/57716