Fatal Error on upgrade-core.php

Getting this error when upgrading (other) plugins

PHP Fatal error occurred: Call to undefined function get_current_screen() in /home/public_html/wp-content/plugins/schema/includes/admin/ref.php on line 120.

From the Codex: This function is defined on most admin pages, but not all. Thus there are cases where is_admin() will return true, but attempting to call get_current_screen() will result in a fatal error because it is not defined. One known example is wp-admin/customize.php.

The function returns null if called from the admin_init hook. It should be OK to use in a later hook such as current_screen.