In CoreUpgrader use global namespace for WP_Error.
In CoreUpgrader use global namespace for WP_Error.

Prevents a fatal error if `$package` is empty.

trepmal/wp-cli,miya0001/wp-cli,GaryJones/wp-cli,GaryJones/wp-cli,gitlost/wp-cli,aaemnnosttv/wp-cli,trepmal/wp-cli,gitlost/wp-cli,miya0001/wp-cli,2ndkauboy/wp-cli,aaemnnosttv/wp-cli,rodrigoprimo/wp-cli,GaryJones/wp-cli,gitlost/wp-cli,trepmal/wp-cli,rodrigoprimo/wp-cli,miya0001/wp-cli,rodrigoprimo/wp-cli,aaemnnosttv/wp-cli,2ndkauboy/wp-cli,2ndkauboy/wp-cli