code: @Beta
    public static <E> ConcurrentHashMultiset<E> create(ConcurrentMap<E, AtomicInteger> countMap) {
      return new ConcurrentHashMultiset<E>(countMap);
    }
docs: Creates a new, empty {@code ConcurrentHashMultiset} using {@code countMap} as the internal
  backing map.
  
  <p>This instance will assume ownership of {@code countMap}, and other code should not maintain
  references to the map or modify it in any way.
  
  <p>The returned multiset is serializable if the input map is.
  
  @param countMap backing map for storing the elements in the multiset and their counts. It must
  be empty.
  @throws IllegalArgumentException if {@code countMap} is not empty
  @since 20.0