can't serialize empty HTML: TypeError: expected string or bytes-like object

[Jakub Wilk]

Apparently lxml.html.parse() can create completely empty tree;
but if you run lxml.html.tostring() on such a tree, it fails with an unhelpful error message:

    >>> doc = lxml.html.parse(open('/dev/null'))
    >>> lxml.html.tostring(doc)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File ".../lib/python3.8/site-packages/lxml/html/__init__.py", line 1873, in tostring
        html = __bytes_replace_meta_content_type(bytes(), html)
    TypeError: expected string or bytes-like object

Version information:

Python : sys.version_info(major=3, minor=8, micro=10, releaselevel='final', serial=0)
lxml.etree : (4, 8, 0, 0)
libxml used : (2, 9, 12)
libxml compiled : (2, 9, 12)
libxslt used : (1, 1, 34)
libxslt compiled : (1, 1, 34)