android/guava/src/com/google/common/collect/Multisets.java
private static <E> boolean addAllImpl(
      Multiset<E> self, AbstractMapBasedMultiset<? extends E> elements) {
    if (elements.isEmpty()) {
      return false;
    }
    elements.addTo(self);
    return true;
  }
private static <E> boolean addAllImpl(
      Multiset<E> self, AbstractMapBasedMultiset<? extends E> elements) {
    if (elements.isEmpty()) {
      return false;
    }
    elements.addTo(self);
    return true;
  }
A specialization of {@code addAllImpl} for when {@code elements} is an
AbstractMapBasedMultiset.