How to fill the required parameters for cipher.doFinal() method in Dart?

In case anyone has encountered this case. This is what I ended up with:

import 'package:pointycastle/export.dart';class Example {  Uint8List encrypt(String data) {    if (data == null || data.length == 0) return null;    final Uint8List _key = utf8.encode('key');    final Uint8List _iv = utf8.encode('iv');    try {      Uint8List encrypted;      final CipherParameters params = PaddedBlockCipherParameters(        ParametersWithIV(          KeyParameter(_key),          _iv,        ),        null,      );      final PaddedBlockCipherImpl cipher = PaddedBlockCipherImpl(        PKCS7Padding(),        CBCBlockCipher(          AESFastEngine(),        ),      );      cipher.init(true, params);      encrypted = cipher.process(utf8.encode(data));      return encrypted;    } catch (_) {      print(_);      return null;    }  }  String decrypt(Uint8List data) {    if (data == null || data.length == 0) return null;    final Uint8List _key = utf8.encode('key');    final Uint8List _iv = utf8.encode('iv');    try {      final CipherParameters params = PaddedBlockCipherParameters(        ParametersWithIV(          KeyParameter(_key),          _iv,        ),        null,      );      final PaddedBlockCipherImpl cipher = PaddedBlockCipherImpl(        PKCS7Padding(),        CBCBlockCipher(          AESFastEngine(),        ),      );      cipher.init(false, params);      final String finalData = utf8.decode(cipher.process(data));      return finalData;    } catch (_) {      print(_);      return null;    }  }}

Thanks to https://stackoverflow.com/users/9014097/topaco and https://github.com/Nguyenpk57 for the inspiration.