Enable to ignore empty child nodes if specified.

# Steps to reproduce this bug
1. Input `<ul><li><a href="#" id="a">a</a></li><li>b</li></ul>`.
2. Select anchor element.
3. Type backspace key twice.


# Expected
* `<p></p><ul><li>b</li></ul>`

or

* `<p><a href="#"></a></p><ul><li>b</li></ul>`


# Result
* `<p><span color="#0000ee" style="color: #0000ee;"><span style="text-decoration: underline;">&nbsp</span></span></p><ul><li>b</li></ul>`