_CastError (Null check operator used on a null value) Error

user_18003111 0
Viewed 58

I have such a code. But I am getting _CastError (Null check operator used on a null value) error in the codes.

const secureStorage = FlutterSecureStorage();
 final encryprionKey = secureStorage.read(key: 'key');
 if (encryprionKey == null) {
   final key = Hive.generateSecureKey();
   await secureStorage.write(
     key: 'key',
     value: base64UrlEncode(key),
   );
 }

 final key = await secureStorage.read(key: 'key');
 final encryptionKey = base64Url.decode(key!);
 print('Encryption key: $encryptionKey');
 final encryptedBox= await Hive.openBox('vaultBox', encryptionCipher: 
 HiveAesCipher(encryptionKey));
 encryptedBox.put('secret', 'Hive is cool');
 print(encryptedBox.get('secret'));

enter image description here

How can I solve it?

dart flutter android
1 Answers

final encryprionKey = secureStorage.read(key: 'key'); neglects to await the result of the secureStorage.read. The returned Future itself is never null, so the if (encryprionKey == null) check is never true, nothing is ever written, and the second secureStorage.read call (which is awaited) will get back null.

This is why the Dart analyzer warned you that the if (encryprionKey == null) condition is always false. Enabling the unawaited_futures lint would have generated an additional (and perhaps clearer) warning.

Not having separate variables for the two calls to secureStorage.read also would have caught this as a compilation error:

  const secureStorage = FlutterSecureStorage();
  var encryprionKey = secureStorage.read(key: 'key');
  if (encryprionKey == null) {
    final key = Hive.generateSecureKey();
    await secureStorage.write(
      key: 'key',
      value: base64UrlEncode(key),
    );
  }

  // This line would have generated a TypeError.
  encryprionKey = await secureStorage.read(key: 'key');

In this case, it'd better to reassign the encryprionKey (sic) variable than to make it final with a separate key variable. Having separate variables to represent the same thing is more confusing and is error-prone.

user_1797150
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