Exemplo ANTES da refatoração do artigo Design Patterns: Null Object.

design-pattern-null-object-article-example-before.ts

interface Logger {
  warn(message: string): void;
}

class ConsoleLogger implements Logger {
  warn(message: string): void {
    console.warn(message);
  }
}

class LoggerFactory {
  factory(env: string): Logger | null {
    if (env === 'development') {
      return new ConsoleLogger();
    }

    return null;
  }
}

class Client {
  execute() {
    const logger = (new LoggerFactory()).factory('production');

    if (logger !== null) {
      logger.warn('It\'s on fire, bicho');
    }
  }
}