code: public V get( Object key )
    {
      int hash = hash( key.hashCode() );
      return segmentFor( hash ).get( key, hash );
    }
docs: Returns the value to which the specified key is mapped,
  or {@code null} if this map contains no mapping for the key.
  <p>
  <p>More formally, if this map contains a mapping from a key
  {@code k} to a value {@code v} such that {@code key.equals(k)},
  then this method returns {@code v}; otherwise it returns
  {@code null}.  (There can be at most one such mapping.)
  
  @throws NullPointerException if the specified key is null