All schema types, not just objects, are permitted as the base type of a resource. A future patch could add validation support for those types, but this fix only prevents a PHP warning from being issued.
Props dhavalkasvala, johnwatkins0, birgire.
Fixes#48785.
git-svn-id: https://develop.svn.wordpress.org/trunk@47328 602fd350-edb4-49c9-b593-d223f7449a82
