<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 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])