code: public V remove(Object key) {
          int hash = hashOf(key);
          return segmentFor(hash).remove(key, hash, null, false);
      }
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