code: public static Function<GHEventsSubscriber, Set<GHEvent>> extractEvents() {
          return new NullSafeFunction<GHEventsSubscriber, Set<GHEvent>>() {
              @Override
              protected Set<GHEvent> applyNullSafe(@Nonnull GHEventsSubscriber subscriber) {
                  return defaultIfNull(subscriber.events(), Collections.<GHEvent>emptySet());
              }
          };
      }
docs: Converts each subscriber to set of GHEvents
  
  @return converter to use in iterable manipulations