code: static <E> boolean addAllImpl(Multiset<E> self, Collection<? extends E> elements) {
      checkNotNull(self);
      checkNotNull(elements);
      if (elements instanceof Multiset) {
        return addAllImpl(self, cast(elements));
      } else if (elements.isEmpty()) {
        return false;
      } else {
        return Iterators.addAll(self, elements.iterator());
      }
    }
docs: An implementation of {@link Multiset#addAll}.