code: public V replace(K key, V value) {
          if (value == null) {
              throw new NullPointerException();
          }
          int hash = this.hashOf(key);
          return this.segmentFor(hash).replace(key, hash, value);
      }
docs: {@inheritDoc}
  
  @return the previous value associated with the specified key, or
  <tt>null</tt> if there was no mapping for the key
  @throws NullPointerException
  if the specified key or value is null