'NoneType' object has no attribute '__dict__'

[njsmith]

@thmo reported this crash when building the pytest docs (apparently they use sphinxcontrib-trio now, I had no idea :-)):

# Sphinx version: 1.7.5
# Python version: 3.6.6 (CPython)
# Docutils version: 0.14 
# Jinja2 version: 2.10
# Last messages:
#   reading sources... [ 89%] projects
#   
#   reading sources... [ 90%] proposals/parametrize_with_fixtures
#   
#   reading sources... [ 91%] pythonpath
#   
#   reading sources... [ 92%] recwarn
#   
#   reading sources... [ 92%] reference
#   
# Loaded extensions:
#   alabaster (0.7.9) from /usr/lib/python3.6/site-packages/alabaster/__init__.py
#   sphinx.ext.autodoc (1.7.5) from /usr/lib/python3.6/site-packages/sphinx/ext/autodoc/__init__.py
#   sphinx.ext.todo (1.7.5) from /usr/lib/python3.6/site-packages/sphinx/ext/todo.py
#   sphinx.ext.autosummary (1.7.5) from /usr/lib/python3.6/site-packages/sphinx/ext/autosummary/__init__.py
#   sphinx.ext.intersphinx (1.7.5) from /usr/lib/python3.6/site-packages/sphinx/ext/intersphinx.py
#   sphinx.ext.viewcode (1.7.5) from /usr/lib/python3.6/site-packages/sphinx/ext/viewcode.py
#   sphinxcontrib_trio (1.0.1) from /usr/lib/python3.6/site-packages/sphinxcontrib_trio/__init__.py
Traceback (most recent call last):
  File "/usr/lib/python3.6/site-packages/sphinx/cmdline.py", line 304, in main
    app.build(args.force_all, filenames)
  File "/usr/lib/python3.6/site-packages/sphinx/application.py", line 331, in build
    self.builder.build_update()
  File "/usr/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 342, in build_update
    'out of date' % len(to_build))
  File "/usr/lib/python3.6/site-packages/sphinx/builders/__init__.py", line 355, in build
    updated_docnames = set(self.env.update(self.config, self.srcdir, self.doctreedir))
  File "/usr/lib/python3.6/site-packages/sphinx/environment/__init__.py", line 565, in update
    self._read_serial(docnames, self.app)
  File "/usr/lib/python3.6/site-packages/sphinx/environment/__init__.py", line 584, in _read_serial
    self.read_doc(docname, app)
  File "/usr/lib/python3.6/site-packages/sphinx/environment/__init__.py", line 659, in read_doc
    doctree = read_doc(self.app, self, self.doc2path(docname))
  File "/usr/lib/python3.6/site-packages/sphinx/io.py", line 294, in read_doc
    pub.publish()
  File "/usr/lib/python3.6/site-packages/docutils/core.py", line 217, in publish
    self.settings)
  File "/usr/lib/python3.6/site-packages/docutils/readers/__init__.py", line 72, in read
    self.parse()
  File "/usr/lib/python3.6/site-packages/docutils/readers/__init__.py", line 78, in parse
    self.parser.parse(self.input, document)
  File "/usr/lib/python3.6/site-packages/sphinx/parsers.py", line 85, in parse
    self.statemachine.run(inputstring, document, inliner=self.inliner)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 171, in run
    input_source=document['source'])
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 239, in run
    context, state, transitions)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 460, in check_line
    return method(match, context, next_state)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2753, in underline
    self.section(title, source, style, lineno - 1, messages)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 327, in section
    self.new_subsection(title, lineno, messages)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 395, in new_subsection
    node=section_node, match_titles=True)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 282, in nested_parse
    node=node, match_titles=match_titles)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 196, in run
    results = StateMachineWS.run(self, input_lines, input_offset)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 239, in run
    context, state, transitions)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 460, in check_line
    return method(match, context, next_state)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2753, in underline
    self.section(title, source, style, lineno - 1, messages)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 327, in section
    self.new_subsection(title, lineno, messages)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 395, in new_subsection
    node=section_node, match_titles=True)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 282, in nested_parse
    node=node, match_titles=match_titles)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 196, in run
    results = StateMachineWS.run(self, input_lines, input_offset)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 239, in run
    context, state, transitions)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 460, in check_line
    return method(match, context, next_state)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2753, in underline
    self.section(title, source, style, lineno - 1, messages)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 327, in section
    self.new_subsection(title, lineno, messages)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 395, in new_subsection
    node=section_node, match_titles=True)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 282, in nested_parse
    node=node, match_titles=match_titles)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 196, in run
    results = StateMachineWS.run(self, input_lines, input_offset)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 239, in run
    context, state, transitions)
  File "/usr/lib/python3.6/site-packages/docutils/statemachine.py", line 460, in check_line
    return method(match, context, next_state)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2326, in explicit_markup
    nodelist, blank_finish = self.explicit_construct(match)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2338, in explicit_construct
    return method(self, expmatch)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2081, in directive
    directive_class, match, type_name, option_presets)
  File "/usr/lib/python3.6/site-packages/docutils/parsers/rst/states.py", line 2130, in run_directive
    result = directive_instance.run()
  File "/usr/lib/python3.6/site-packages/sphinx/ext/autodoc/directive.py", line 133, in run
    documenter.generate(more_content=self.content)
  File "/usr/lib/python3.6/site-packages/sphinx/ext/autodoc/__init__.py", line 747, in generate
    if not self.import_object():
  File "/usr/lib/python3.6/site-packages/sphinxcontrib_trio/__init__.py", line 350, in import_object
    obj = self.parent.__dict__.get(self.object_name)
AttributeError: 'NoneType' object has no attribute '__dict__'

From a quick skim, I think the issue is that somehow autodoc was trying to look up an unknown method (e.g. .. automethod:: SomeClass.misspelled_nmae), and we're crashing instead of reporting a proper error message.

Specifically, it looks like we need to port this fix: sphinx-doc/sphinx@1d742bd into sphinxcontrib-trio's version of MethodDocumentor.import_object

Well, I'm not entirely sure whether that's the actual issue because I'm not sure what exactly @thmo was doing or how to reproduce it, but this seems like a good idea regardless :-)