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http://url.spec.whatwg.org/#urlutils-and-urlutilsreadonly-members [[ If object's url object is not null, set object to a new URLObject object using object. ]] It's not URLObject but URLQuery.
Thanks! https://github.com/whatwg/url/commit/aa76b40ab9f8d74427b1f0345a661d6fa8024dd6