def _convert_types(self, filename: str, df: pd.DataFrame) -> None:
        """
        Apply type conversions
        """
        if df.empty:
            return

        converters = self._config.nodes.get(filename, {}).get("converters", {})
        for col, converter in converters.items():
            if col in df.columns:
                df[col] = converter(df[col])
Apply type conversions