anchor.diff:  
   String decrypt(String data, String key) {
       initSymCrypt();
  -    if (data == null || data == "") {
  +    if (data == null || data.isEmpty) {
         return null;
       }
       Uint8List _key = new Uint8List.fromList(key.codeUnits);
  
positive.code: 
  String encrypt(String data, String key) {
      initSymCrypt();
      if (data == null || data == "") {
        return null;
      }
      Uint8List _key = new Uint8List.fromList(key.codeUnits);
  
negative.code:   }
  
  
  String saltData(String data, String salt) {
      if (data.isEmpty || salt.isEmpty) {
        return data;
      }
      String _data = data + salt;
      var sha256 = new MD5();
  