ParseDataFormat, rf_names[0].rf is actualy RESTResponseFormat::UNDEF:
https://github.com/bitcoin/bitcoin/blob/e3f416dbf7633b2fb19c933e5508bd231cc7e9cf/src/rest.cpp#L48-L57
so it would be more clarity and code readability to use return RESTResponseFormat::UNDEF; to replace return rf_names[0].rf;