def find_first_version(self):
        """Finds the first version of igraph that exists in the nightly build
        repo from the version numbers provided in ``self.versions_to_try``."""
        for version in self.versions_to_try:
            remote_url = self.get_download_url(version=version)
            if http_url_exists(remote_url):
                return version, remote_url
        return None, None
Finds the first version of igraph that exists in the nightly build
        repo from the version numbers provided in ``self.versions_to_try``.