validate property

Implementation

@override
String? get validate {
  final List<String?> param = [secret, seed, seedHex, passphrase];
  param.removeWhere((element) => element == null);
  if (param.length != 1) {
    return "sing Must have only one of secret, seed, seedHex, and passphrase.";
  }
  if (secret != null && keyType != null) {
    return "Must omit keyType if secret is provided.";
  }
  return null;
}