Empty tuple annotation causes crash

[mwchase]

I have some functions that deal with unions where one variant is the empty tuple. Per python/mypy#4211, the way to represent the empty tuple type is typing.Tuple[()]. Using this annotation crashes flake8-annotations-complexity with the following traceback:

Traceback (most recent call last):
  File "/Users/maxchase/.pyenv/versions/structured-data/bin/flake8", line 10, in <module>
    sys.exit(main())
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/main/cli.py", line 18, in main
    app.run(argv)
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/main/application.py", line 393, in run
    self._run(argv)
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/main/application.py", line 381, in _run
    self.run_checks()
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/main/application.py", line 300, in run_checks
    self.file_checker_manager.run()
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/checker.py", line 331, in run
    self.run_serial()
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/checker.py", line 315, in run_serial
    checker.run_checks()
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/checker.py", line 598, in run_checks
    self.run_ast_checks()
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8/checker.py", line 502, in run_ast_checks
    for (line_number, offset, text, check) in runner:
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/checker.py", line 25, in run
    self.max_annotations_complexity,
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/ast_helpres.py", line 28, in validate_annotations_in_ast_node
    complexity = get_annotation_compexity(annotation)
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/ast_helpres.py", line 9, in get_annotation_compexity
    return 1 + get_annotation_compexity(annotation_node.slice.value)  # type: ignore
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/ast_helpres.py", line 11, in get_annotation_compexity
    return max(get_annotation_compexity(n) for n in annotation_node.elts)
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/ast_helpres.py", line 11, in <genexpr>
    return max(get_annotation_compexity(n) for n in annotation_node.elts)
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/ast_helpres.py", line 9, in get_annotation_compexity
    return 1 + get_annotation_compexity(annotation_node.slice.value)  # type: ignore
  File "/Users/maxchase/.pyenv/versions/3.7.4/envs/structured-data/lib/python3.7/site-packages/flake8_annotations_complexity/ast_helpres.py", line 11, in get_annotation_compexity
    return max(get_annotation_compexity(n) for n in annotation_node.elts)
ValueError: max() arg is an empty sequence

I can put in a PR for this.

[Melevir]

Thanks for the report. It would be nice to see PR with fix of the bug.
Please, add test for this case.