langchain/document_loaders/blackboard.py/BlackboardLoader/_get_paths
class BlackboardLoader:    def _get_paths(self, soup: Any) -> List[str]:
        """Get all relative paths in the navbar."""
        relative_paths = []
        course_menu = soup.find("ul", {"class": "courseMenu"})
        if course_menu is None:
            raise ValueError("No course menu found.")
        for link in course_menu.find_all("a"):
            href = link.get("href")
            if href is not None and href.startswith("/"):
                relative_paths.append(href)
        return relative_paths