code: @Override
      public V remove(Object key) {
          int hash = hash(key);
          Segment<K,V> s = segmentForHash(hash);
          return s == null ? null : s.remove(key, hash, null);
      }
docs: Removes the key (and its corresponding value) from this map.
  This method does nothing if the key is not in the map.
  
  @param  key the key that needs to be removed
  @return the previous value associated with <tt>key</tt>, or
  <tt>null</tt> if there was no mapping for <tt>key</tt>
  @throws NullPointerException if the specified key is null