test suite fails with sending None to string2lines() in Sphinx

[mcepl]

While packaging breathe for openSUSE 4.35.0 and with Sphinx 7.4.5 I found that 13 tests (out of 21) failed because apparently they are sending something wrong to Sphinx so that string2lines ends up with None instead of string or bytes:

[   20s] _______________________________ test_render_func _______________________________
[   20s] 
[   20s] app = <SphinxTestApp buildername='html'>
[   20s] 
[   20s]     def test_render_func(app):
[   20s]         member_def = WrappedMemberDef(
[   20s]             kind="function",
[   20s]             definition="void foo",
[   20s]             type_="void",
[   20s]             name="foo",
[   20s]             argsstring="(int)",
[   20s]             virt="non-virtual",
[   20s]             param=[
[   20s]                 WrappedParam(type_=WrappedLinkedText(content_=[WrappedMixedContainer(value="int")]))
[   20s]             ],
[   20s]         )
[   20s] >       signature = find_node(render(app, member_def), "desc_signature")
[   20s] 
[   20s] tests/test_renderer.py:335: 
[   20s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[   20s] tests/test_renderer.py:320: in render
[   20s]     return renderer.render(member_def)
[   20s] ../../BUILDROOT/python-breathe-4.35.0-0.x86_64/usr/lib/python3.10/site-packages/breathe/renderer/sphinxrenderer.py:2624: in render
[   20s]     result = method(self, node)
[   20s] ../../BUILDROOT/python-breathe-4.35.0-0.x86_64/usr/lib/python3.10/site-packages/breathe/renderer/sphinxrenderer.py:2511: in dispatch_memberdef
[   20s]     return self.visit_function(node)
[   20s] ../../BUILDROOT/python-breathe-4.35.0-0.x86_64/usr/lib/python3.10/site-packages/breathe/renderer/sphinxrenderer.py:2003: in visit_function
[   20s]     nodes = self.handle_declaration(node, declaration)
[   20s] ../../BUILDROOT/python-breathe-4.35.0-0.x86_64/usr/lib/python3.10/site-packages/breathe/renderer/sphinxrenderer.py:667: in handle_declaration
[   20s]     nodes_ = self.run_directive(obj_type, declaration, content_callback, options)
[   20s] ../../BUILDROOT/python-breathe-4.35.0-0.x86_64/usr/lib/python3.10/site-packages/breathe/renderer/sphinxrenderer.py:619: in run_directive
[   20s]     nodes = directive.run()
[   20s] /usr/lib/python3.10/site-packages/sphinx/domains/cpp/__init__.py:319: in run
[   20s]     return super().run()
[   20s] /usr/lib/python3.10/site-packages/sphinx/directives/__init__.py:281: in run
[   20s]     content_children = self.parse_content_to_nodes(allow_section_headings=True)
[   20s] /usr/lib/python3.10/site-packages/sphinx/util/docutils.py:415: in parse_content_to_nodes
[   20s]     return nested_parse_to_nodes(
[   20s] /usr/lib/python3.10/site-packages/sphinx/util/parsing.py:55: in nested_parse_to_nodes
[   20s]     content = _text_to_string_list(
[   20s] /usr/lib/python3.10/site-packages/sphinx/util/parsing.py:92: in _text_to_string_list
[   20s]     content = string2lines(text, tab_width, convert_whitespace=True)
[   20s] _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
[   20s] 
[   20s] astring = None, tab_width = 8, convert_whitespace = True
[   20s] whitespace = re.compile('[\x0b\x0c]')
[   20s] 
[   20s]     def string2lines(astring, tab_width=8, convert_whitespace=False,
[   20s]                      whitespace=re.compile('[\v\f]')):
[   20s]         """
[   20s]         Return a list of one-line strings with tabs expanded, no newlines, and
[   20s]         trailing whitespace stripped.
[   20s]     
[   20s]         Each tab is expanded with between 1 and `tab_width` spaces, so that the
[   20s]         next character's index becomes a multiple of `tab_width` (8 by default).
[   20s]     
[   20s]         Parameters:
[   20s]     
[   20s]         - `astring`: a multi-line string.
[   20s]         - `tab_width`: the number of columns between tab stops.
[   20s]         - `convert_whitespace`: convert form feeds and vertical tabs to spaces?
[   20s]         - `whitespace`: pattern object with the to-be-converted
[   20s]           whitespace characters (default [\\v\\f]).
[   20s]         """
[   20s]         if convert_whitespace:
[   20s] >           astring = whitespace.sub(' ', astring)
[   20s] E           TypeError: expected string or bytes-like object
[   20s] 
[   20s] /usr/lib/python3.10/site-packages/docutils/statemachine.py:1506: TypeError
[   20s] --------------------------- Captured stdout teardown ---------------------------
[   20s] # testroot: root
[   20s] # builder: html
[   20s] # srcdir: /tmp/pytest-of-abuild/pytest-0/root
[   20s] # outdir: /tmp/pytest-of-abuild/pytest-0/root/_build/html
[   20s] # status: 
[   20s] �[01mRunning Sphinx v7.4.5�[39;49;00m
[   20s] �[01mloading translations [en]... �[39;49;00mdone
[   20s] 
[   20s] # warning: 
[   20s] 

Complete build log with all packages used and steps to produce the reproduction