TypeError: Cannot read properties of undefined (reading 'toLowerCase') in parseHTML of codeblock

[Karl-Wu]

Describe the bug
Got TypeError: Cannot read properties of undefined (reading 'toLowerCase') while calling tryParseHTMLToBlocks.
The HTML is not well-formed which was converted by readability.js.

To Reproduce

1. Open the following link
   https://stackblitz.com/edit/github-xpg9ndgd?file=package.json,html-with-codeblock.ts,App.tsx
2. Check the output of dev console

Misc

• Node version:
• Package manager:
• Browser:
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