def METHOD_NAME(self, subj: str, rel: str, obj: str) -> None:
    """Add triplet."""
    if subj not in self._data.graph_dict:
        self._data.graph_dict[subj] = []
    if (rel, obj) not in self._data.graph_dict[subj]:
        self._data.graph_dict[subj].append([rel, obj])