code: @SuppressWarnings("unchecked")
  	static <T> void subscribe(CoreSubscriber<? super T> s, Iterator<? extends T> it) {
  		subscribe(s, it, null);
  	}
docs: Common method to take an Iterator as a source of values.
  
  @param s the subscriber to feed this iterator to
  @param it the iterator to use as a source of values