AttributeError: type object 'InvalidCastOption' has no attribute '__code__' with Sphinx 3.2.0

[flazzarini]

Describe the bug
With the latest version of Sphinx 3.2.0 I am getting the following error when trying to render my documentation. The error doesn't appear with version 3.1.2.

To Reproduce
The project in which this happens is a private project. But here is the complete traceback of the error that appears.

# Sphinx version: 3.2.0
# Python version: 3.5.2 (CPython)
# Docutils version: 0.16 release
# Jinja2 version: 2.11.2
# Last messages:
#   reading sources... [ 14%] api/foobar.cli
#   
#   reading sources... [ 18%] api/foobar.cli.retry_failed_orders
#   
#   reading sources... [ 22%] api/foobar.config
#   
#   reading sources... [ 25%] api/foobar.const
#   
#   reading sources... [ 29%] api/foobar.exc
#   
# Loaded extensions:
#   sphinxcontrib.devhelp (1.0.2) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinxcontrib/devhelp/__init__.py
#   sphinx.ext.autodoc.type_comment (3.2.0) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/type_comment.py
#   sphinx.ext.autodoc (3.2.0) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py
#   sphinxcontrib.qthelp (1.0.3) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinxcontrib/qthelp/__init__.py
#   sphinx.ext.extlinks (3.2.0) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/extlinks.py
#   sphinxcontrib.serializinghtml (1.1.4) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinxcontrib/serializinghtml/__init__.py
#   alabaster (0.7.12) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/alabaster/__init__.py
#   sphinx.ext.mathjax (3.2.0) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/mathjax.py
#   sphinxcontrib.applehelp (1.0.2) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinxcontrib/applehelp/__init__.py
#   sphinxcontrib.htmlhelp (1.0.3) from /home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinxcontrib/htmlhelp/__init__.py
Traceback (most recent call last):
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/cmd/build.py", line 280, in build_main
    app.build(args.force_all, filenames)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/application.py", line 348, in build
    self.builder.build_update()
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 299, in build_update
    len(to_build))
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 311, in build
    updated_docnames = set(self.read())
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 418, in read
    self._read_serial(docnames)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 439, in _read_serial
    self.read_doc(docname)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/builders/__init__.py", line 479, in read_doc
    doctree = read_doc(self.app, self.env, self.env.doc2path(docname))
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/io.py", line 223, in read_doc
    pub.publish()
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/core.py", line 218, in publish
    self.settings)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/io.py", line 128, in read
    self.parse()
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/readers/__init__.py", line 77, in parse
    self.parser.parse(self.input, document)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/parsers.py", line 102, in parse
    self.statemachine.run(inputlines, document, inliner=self.inliner)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 171, in run
    input_source=document['source'])
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/statemachine.py", line 242, in run
    context, state, transitions)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/statemachine.py", line 459, in check_line
    return method(match, context, next_state)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 2769, in underline
    self.section(title, source, style, lineno - 1, messages)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 327, in section
    self.new_subsection(title, lineno, messages)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 395, in new_subsection
    node=section_node, match_titles=True)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 282, in nested_parse
    node=node, match_titles=match_titles)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 196, in run
    results = StateMachineWS.run(self, input_lines, input_offset)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/statemachine.py", line 242, in run
    context, state, transitions)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/statemachine.py", line 459, in check_line
    return method(match, context, next_state)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 2342, in explicit_markup
    nodelist, blank_finish = self.explicit_construct(match)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 2354, in explicit_construct
    return method(self, expmatch)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 2097, in directive
    directive_class, match, type_name, option_presets)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/docutils/parsers/rst/states.py", line 2146, in run_directive
    result = directive_instance.run()
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/directive.py", line 146, in run
    documenter.generate(more_content=self.content)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 894, in generate
    self.document_members(all_members)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 777, in document_members
    check_module=members_check_module and not isattr)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 1570, in generate
    all_members=all_members)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 894, in generate
    self.document_members(all_members)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 1559, in document_members
    super().document_members(all_members)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 777, in document_members
    check_module=members_check_module and not isattr)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 884, in generate
    self.add_directive_header(sig)
  File "/home/users/frank/workspace/foobar/env/lib/python3.5/site-packages/sphinx/ext/autodoc/__init__.py", line 1980, in add_directive_header
    annotations = get_type_hints(self.parent)
  File "/usr/lib/python3.5/typing.py", line 1177, in get_type_hints
    defaults = _get_defaults(obj)
  File "/usr/lib/python3.5/typing.py", line 1134, in _get_defaults
    code = func.__code__
AttributeError: type object 'InvalidCastOption' has no attribute '__code__'

Expected behavior
Documentation should be rendered.

Your project
Can't link the project.

Environment info

• OS: Linux
• Python version: 3.5.2
• Sphinx version: 3.2
• Sphinx extensions: [sphinx.ext.autodoc, sphinx.ext.extlinks]

[exhuma]

I can confirm that I have the same issue with the latest version of Sphinx.