修复不可为空的Dartz包

import 'package:dartz/dartz.dart';

class Example {
  final int id;
  final String? name; // 使用 ? 表示可空

  Example(this.id, this.name);
}

Example(int id, String? name) : id = id, name = name ?? ''; // 提供默认值

dependencies:
  dartz: ^最新版本号

import 'package:dartz/dartz.dart';

final name = Option<String>.fromNullable(someValue);

final name = example.name.getOrElse(() => 'Default Name');

import 'package:dartz/dartz.dart';

class User {
  final int id;
  final String name;
  final Option<String> email; // 使用 Option 类型处理可空字段

  User(this.id, this.name, this.email);

  String getDisplayName() {
    return email.getOrElse(() => 'No Email').isEmpty ? name : '$name (${email.getOrElse(() => '')})';
  }
}

void main() {
  final user1 = User(1, 'Alice', Some('alice@example.com'));
  final user2 = User(2, 'Bob', None());

  print(user1.getDisplayName()); // 输出: Alice (alice@example.com)
  print(user2.getDisplayName()); // 输出: Bob (No Email)
}