Description

--wp--style--block-gap: ; and margin-block-start: ; are generated for .wp-site-blocks) when using blockGap: null; in theme.json, this results in the w3c validator showing a CSS error

Step-by-step reproduction instructions

• set blockGap: null; in theme.json on settings section
• add a few blocks to a post or page, like calendar and search
• open the page/post
• check the inline styles in global-styles-inline-css
• the css rule is generated with an empty value: :where(.wp-site-blocks) > * { margin-block-start: ; margin-block-end: 0; }

Screenshots, screen recording, code snippet

Environment info

• WordPress 6.8
• Gutenberg 21.5
• Theme 2025

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure