Cleaner.clean_html is buggy on simple HTML

[X]

Python : sys.version_info(major=3, minor=9, micro=12, releaselevel='final', serial=0)
lxml.etree : (4, 9, 2, 0)
libxml used : (2, 9, 14)
libxml compiled : (2, 9, 4)
libxslt used : (1, 1, 35)
libxslt compiled : (1, 1, 35)

The following code triggers the bug:

from lxml.html.clean import Cleaner
c = Cleaner()

c.clean_html("<li></li>")

The behavior is the following:

>>> import lxml
>>> lxml.__version__
'4.9.2'
>>> from lxml.html.clean import Cleaner
>>> c = Cleaner()
>>>
>>> c.clean_html("<li></li>")
'<li>'