ast.get_docstring: wrong return type

[blueyed]

At least in recent Python versions it can return None: https://github.com/python/cpython/blob/0705ec8a149e27023b0420ae0366d16255f6c9f7/Lib/ast.py#L270-L293

typed_ast also seems to be affected, but has Optional[bytes] already:

stdlib/3/ast.pyi
194:def get_docstring(node: AST, clean: bool = ...) -> str: ...

third_party/3/typed_ast/ast27.pyi
15:def get_docstring(node: AST, clean: bool = ...) -> Optional[bytes]: ...

third_party/3/typed_ast/ast3.pyi
15:def get_docstring(node: AST, clean: bool = ...) -> str: ...

stdlib/2/ast.pyi
16:def get_docstring(node: AST, clean: bool = ...) -> str: ...

(@ 675ab77)

[JelleZijlstra]

Looks like you're right, feel free to submit a PR.