Can't remove a single empty code-block with Backspace

[ViktorZhurbin]

Please help me out if it's a bug or a feature. To me it's unexpected.

Steps for Reproduction

1. Visit https://quilljs.com/playground/snow
2. Using the basic example, insert an empty code block in editor
3. Only an empty code block is in the editor, nothing else
4. Hit Backspace

Expected behavior: Code block is removed

Actual behavior: Code block stays there