def add_header(self, key: str, val: str) -> None:
        """Cookielib has no legitimate use for this method.

        Add it back if you find one.
        """
        raise NotImplementedError(
            "Cookie headers should be added with add_unredirected_header()"
        )
Cookielib has no legitimate use for this method.

        Add it back if you find one.
        
grab/util/cookies.py