Undefined index during automatic plugin/theme updates

[afragen]

When a site has only plugins or themes available for auto-updates the WP_Automatic_Updater::after_plugin_theme_update( $update_results ) may have an undefined value in the parameter $update_results. This will result in a PHP Notice for an undefined index of either 'plugin' or 'theme' in wp-admin/includes/class-wp-automatic-updater in the auto_{plugin|theme}_update_send_email filter hook.

To fix this, the missing index simply needs to be set.

[audrasjb]

Good catch @afragen

Indeed, this is a real issue. The patch looks good to me.
Let's move this to 5.5.2.

[audrasjb]

As per @peterwilsoncc’s comment during today’s bug scrub, let's see if we can define each sub array while setting up rather than isset checks. Otherwise, the current patch is tested and works fine.

[SergeyBiryukov]

In 49166:

Upgrade/Install: Check if plugin or theme update results are available before applying the notification filters.

This avoids a PHP notice for an undefined index of either plugin or theme in the auto_{plugin|theme}_update_send_email filter hook.

Props afragen, audrasjb.
Fixes #51400.

[SergeyBiryukov]

In 49167:

Upgrade/Install: Check if plugin or theme update results are available before applying the notification filters.

This avoids a PHP notice for an undefined index of either plugin or theme in the auto_{plugin|theme}_update_send_email filter hook.

Props afragen, audrasjb.
Merges [49166] to the 5.5 branch.
Fixes #51400.