def get_gold_labels(self, cand_lists, annotator=None):
return get_sparse_matrix(self.session, GoldLabelKey, cand_lists, key=annotator)<EOL>
Load sparse matrix of GoldLabels for each candidate_class.

        :param cand_lists: The candidates to get gold labels for.
        :type cand_lists: List of list of candidates.
        :param annotator: A specific annotator key to get labels for. Default
            None.
        :type annotator: str
        :return: A list of MxN sparse matrix where M are the candidates and N is the
            annotators. If annotator is provided, return a list of Mx1 matrix.
        :rtype: list[csr_matrix]