code: boolean replace(K key, long expectedOldValue, long newValue) {
      if (expectedOldValue == 0L) {
        return putIfAbsent(key, newValue) == 0L;
      } else {
        return map.replace(key, expectedOldValue, newValue);
      }
    }
docs: If {@code (key, expectedOldValue)} is currently in the map, this method replaces {@code
  expectedOldValue} with {@code newValue} and returns true; otherwise, this method returns false.
  
  <p>If {@code expectedOldValue} is zero, this method will succeed if {@code (key, zero)} is
  currently in the map, or if {@code key} is not in the map at all.