Cannot read properties of null (reading 'tagName') when using happy-dom

Hello, I found this issue when parsing some specific HTML markup; I'm not sure what the root cause is.

Reproduction

const { Readability } = require('@mozilla/readability')
const { Browser } = require('happy-dom')

const path = require('path')
const fs = require('fs')

// https://github.com/microlinkhq/metascraper/blob/master/packages/metascraper-readability/test/fixtures/chowhanandsons.com.html
const html = fs.readFileSync(
  path.join(__dirname, 'packages/metascraper-readability/test/fixtures/chowhanandsons.com.html'),
  'utf-8'
)

const getDocument = ({ url, html }) => {
  const browser = new Browser({
    settings: {
      disableComputedStyleRendering: true,
      disableCSSFileLoading: true,
      disableIframePageLoading: true,
      disableJavaScriptEvaluation: true,
      disableJavaScriptFileLoading: true
    }
  })

  const page = browser.newPage()
  page.url = url
  page.content = html
  return {
    document: page.mainFrame.document,
    teardown: () => browser.close()
  }
}

const url = ' https://www.chowhanandsons.com/'

const { document, teardown } = getDocument({ url, html })
const reader = new Readability(document)
console.log(reader.parse())
teardown()

Start by reproducing the failure with packages/metascraper-readability/test/fixtures/chowhanandsons.com.html, happy-dom, and Readability.parse(). Trace the null value to determine why tagName is accessed during parsing. Done means this fixture no longer triggers the TypeError and the behavior is covered by a regression check.