title: @Async in spring mvc working without a Future return type?
body: <p>Sometimes when I am using @Async without return type of Future it returns null but sometimes it returns String. In documentation it is mentioned that return type of Future is must. I am confused why this is happening?</p>
  
  <p>e.g.this one is working</p>
  
  <pre><code>@Service
  public class MyClass implements MyClass2{
  
    @Async
    @Override
    public String getString() {
  
      return "hello";
    }
  }
  </code></pre>