/*
   * Cache the size for efficiency. Using a long lets us avoid the need for
   * overflow checking and ensures that size() will function correctly even if
   * the multiset had once been larger than Integer.MAX_VALUE.
   */
  private transient long size;

  /** Standard constructor. */
  protected AbstractMapBasedMultiset(Map<E, Count> backingMap) {
    checkArgument(backingMap.isEmpty());