anchor.diff:      return hexString;
     }
   
  -String createHash([String str = ""]) {
  -    if (str == null) {
  -      str = "";
  -    }
  +String createHash(String str) {
       MD5 sha256 = new MD5();
  -    sha256.add(str.codeUnits);
  +    sha256.add(str?.codeUnits);
       var digest = sha256.close();
       var hexString = CryptoUtils.bytesToBase64(digest);
       return hexString;
  
positive.code: 
  String decrypt(String data, String key) {
      initSymCrypt();
      if (data == null || data == "") {
        return null;
      }
      Uint8List _key = new Uint8List.fromList(key.codeUnits);
  
negative.code: 
  String encrypt(String data, String key) {
      initSymCrypt();
      if (data == null || data.isEmpty) {
        return null;
      }
      Uint8List _key = new Uint8List.fromList(key.codeUnits);
  