code: public void addColl(Collection<E> collection) {
  		if (current == null) {
  			current = collection.iterator();
  		} else {
  			collections.add(collection);
  		}
  	}
docs: Adds a collection to the merged iterator. The iterator of the
  collection is only requested after other iterators are exhausted.
  This can help avoiding concurrent modification exceptions.
  
  @param collection The collection that should be added to the iterator.