How to know a Otto Subscriber is registered

I am using Otto by Square. My subscriber class is registered in the Activity / Fragment onStart and onStop methods.

However sometimes, I get this error

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)

I am pretty sure my class is registered. Is there a method to know if this class is registered or not ?

// 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(); // ??
}

Like @laalto said there is no such method in Bus API. Here is how I implemented the boolean isRegistered

//  implement as a Singleton class
public class EventListener {

    // necessary to avoid to unregister a non-registered instance . Since EventListener is a Singleton
    private static boolean isRegistered;

    public void setIsRegistered(final boolean registered){
        isRegistered = registered;
    }

    public boolean isRegistered(){
        return isRegistered;
    }

    @Subscribe
    public void onTrackingEvent(final TrackingEvent event) {
        // to do
    }
}

Now in the Fragment or Activity, register/unregister to the com.squareup.otto.Bus

// in a Fragment or Activity
@Override
public void onStart() {
    super.onStart();
    // eventListener is the class containing the @Subscribe method
    bus.register(eventListener);
    eventListener.setIsRegistered(true);
}

@Override
public void onStop() {
    super.onStop();
    if (eventListener.isRegistered()) {
        bus.unregister(eventListener);
        eventListener.setIsRegistered(false);
    }
}