def METHOD_NAME(self, config: Dict, prefix: Optional[str] = None) -> Dict:
    """Applied this version transformation to a specified prefix of the config, returns the updated config. If
    prefix names a list, i.e. "input_features", applies the transformation to each list element (input
    feature).
    Args:
        config: A config dictionary.
        prefix: An optional keypath prefix i.e. "input_features". If no prefix specified, transformation is applied
                to config itself.
    Returns The updated config.
    """
    if prefix:
        components = prefix.split(".", 1)
        key = components[0]
        rest_of_prefix = components[1] if len(components) > 1 else ""
        if key in config:
            subsection = config[key]
            if isinstance(subsection, list):
                config[key] = [
                    self.METHOD_NAME(v, prefix=rest_of_prefix) if isinstance(v, dict) else v
                    for v in subsection
                ]
            elif isinstance(subsection, dict):
                config[key] = self.METHOD_NAME(subsection, prefix=rest_of_prefix)
        return config
    else:
        # Base case: no prefix specified, pass entire dictionary to transform function.
        transformed_config = self.transform(config)
        if transformed_config is None:
            logger.error("Error: version transformation returned None. Check for missing return statement.")
        return transformed_config