android/guava/src/com/google/common/collect/ConcurrentHashMultiset.java
@Beta
  public static <E> ConcurrentHashMultiset<E> create(ConcurrentMap<E, AtomicInteger> countMap) {
    return new ConcurrentHashMultiset<E>(countMap);
  }
@Beta
  public static <E> ConcurrentHashMultiset<E> create(ConcurrentMap<E, AtomicInteger> countMap) {
    return new ConcurrentHashMultiset<E>(countMap);
  }
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