setDelta method 
    
    
    
  Implementation
  @override
Future<bool> setDelta({
  required String directive,
  required String mid,
  required Map<String, dynamic>? delta,
}) async {
  await initialize();
  Map<String, dynamic> input = makeData(directive: directive, mid: mid, delta: delta);
  logger.finest('setDelta = ${input.toString()}');
  try {
    await _db!.child('hycop_delta').child(mid).set(input);
    logger.finest("hycop_delta sample data created");
    return true;
  } catch (e) {
    logger.severe("hycop_delta SET DB ERROR : $e");
    return false;
  }
}