In set_theme_mod() account for when there is no old value.

fixes #14721. see [27393].

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Restyles the modal for attaching media to posts, take II (also some autoprefixer and imagemin). Props avryl, see #26952.
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Add a `class` attribute to the caption shortcode to allow for additional classes on the caption container. props rhyswynne, mcadwell. fixes #25295.

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Always convert auto-drafts to drafts in edit_draft() and _wp_translate_postdata().

This regressed due to refactoring in [26995]. This commit fixes Quick Draft.

see #25272.

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Multisite load: Properly call wp_cache_set().

props gradyetc.
see #27003.

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Deprecate get_current_site_name(). see #27003.

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