def find_by_id(self, user_id):
        user_file = self._id_index.get(user_id)
        if user_file is None:
            return None

        return self._load_user(user_file)
Find a user by their ID or return ``None``.
dataset/ETHPy150Open mblayman/markwiki/markwiki/storage/fs/user.py/FileUserStorage.find_by_id