Fixes the error handling for when `WP_Classic_To_Block_Menu_Converter::convert()` returns an instance of `WP_Error`.
`WP_Navigation_Fallback::create_classic_menu_fallback()` now checks for `is_wp_error()` and if `true`, returns the error. And the `@return` type is updated to
`string|WP_Error`.
Also includes a fix in the return type in `WP_Classic_To_Block_Menu_Converter::convert()` to return an empty string instead of an array instead, i.e. when bailing
out for no menu items returned by `wp_get_nav_menu_items()`. The return type is clearly documented as a string.
Follow-up to [56052].
Props dlh, get_dave, antonvlasenko, hellofromTonya.
Reviewed by azaozz, audrasjb.
Merges [56422] to the 6.3 branch.
Fixes#58823.
--Cette ligne, et les suivantes ci-dessous, seront
ignorées--
_M .
M src/wp-includes/class-wp-classic-to-block-menu-converter.php
M src/wp-includes/class-wp-navigation-fallback.php
M tests/phpunit/tests/editor/classic-to-block-menu-converter.php
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