docs: protected Object execute(final Job job, final String curQueue, final Object instance) throws Exception {
          if (instance instanceof WorkerAware) {
              ((WorkerAware) instance).setWorker(this);
          }
          this.listenerDelegate.fireEvent(JOB_EXECUTE, this, curQueue, job, instance, null, null);
          final Object result;
          if (instance instanceof Callable) {
              result = ((Callable<?>) instance).call(); // The job is executing!
          } else if (instance instanceof Runnable) {
              ((Runnable) instance).run(); // The job is executing!
              result = null;
          } else { // Should never happen since we're testing the class earlier
              throw new ClassCastException(
                      "Instance must be a Runnable or a Callable: " + instance.getClass().getName() + " - " + instance);
          }
          return result;
      }