If the getpath.joinpath() is called without arguments, it tries to return an empty string and calls PyUnicode_FromString(NULL) for this, which causes a crash. The correct way of creating an empty string is PyUnicode_FromStringAndSize(NULL, 0), or PyUnicode_FromString(""), or PyUnicode_FromStringAndSize("", 0).

Alternatively, the function could raise a TypeError instead of returning an empty string.

@zooba @vstinner