title: libGDX: Check if actor exists fails with NullPointerException
body: <p>I am trying to check if an actor exists but have no luck so far. My code looks like this:</p>
  
  <pre><code>if (prize.getStage() == null)
       System.out.println("not on stage");
  else
       System.out.println("on stage");
  </code></pre>
  
  <p>According to the answer in this link:
  <a href="https://stackoverflow.com/questions/33270598/libgdx-how-check-if-the-actor-exist-on-stage-or-not">libGDX : How check if the actor exist on stage or not</a></p>
  
  <p>But I receive the following error:
  "LWJGL Application" java.lang.NullPointerException</p>
  
  <p>Does anyone know what I am doing wrong or if there is another good way to check if an actor is on stage?</p>