code: public static <K, V> ConcurrentMap<K, V> newConcurrentMap() {
      return new MapMaker().<K, V>makeMap();
    }
docs: Returns a general-purpose instance of {@code ConcurrentMap}, which supports
  all optional operations of the ConcurrentMap interface. It does not permit
  null keys or values. It is serializable.
  
  <p>This is currently accomplished by calling {@link MapMaker#makeMap()}.
  
  <p>It is preferable to use {@code MapMaker} directly (rather than through
  this method), as it presents numerous useful configuration options,
  such as the concurrency level, load factor, key/value reference types,
  and value computation.
  
  @return a new, empty {@code ConcurrentMap}
  @since 3.0