When `document.importNode` is used to create elements that have a null registry, the resulting elements have an incorrect registry when importNode does not specify a registry. This should create elements with `customElementRegistry` set to the document default registry (e.g. window.customElements), but instead it is set to `undefined`, which incorrect and an invalid value. See reproduction (asserts in console): https://codepen.io/Steve-Orvell/pen/MYeRmQM?editors=0010