title: How to know a Otto Subscriber is registered
body: <p>I am using <a href="http://square.github.io/otto/" rel="nofollow">Otto</a> by Square. My subscriber class is registered in the Activity / Fragment <code>onStart</code> and <code>onStop</code> methods.</p>
  
  <p>However sometimes, I get this error</p>
  
  <blockquote>
    <p>Caused by: java.lang.IllegalArgumentException: Missing event handler
    for an annotated method. Is class EventListener registered?
    at com.squareup.otto.Bus.unregister(Bus.java:289)</p>
  </blockquote>
  
  <p>I am pretty sure my class is registered. Is there a method to know if this class is registered or not ?</p>
  
  <pre><code>// in a Fragment or Activity
  @Override
  public void onStart() {
      super.onStart();
  
      Bus bus = new Bus();
      bus.register(eventListener); // register the class where the annotated @Subscribe method is
      bus.isRegistered(); // ??
  }
  </code></pre>