def METHOD_NAME(self) -> str:
    if self._private_key:
        return self._private_key
    if self._private_key_path:
        if not Path(self._private_key_path).is_file():
            raise OgrException(
                f"File with the github-app private key "
                f"({self._private_key_path}) "
                f"does not exist."
            )
        return Path(self._private_key_path).read_text()
    return None