code: public final Node popAndTop()
    {
  
      m_firstFree--;
  
      m_map[m_firstFree] = null;
  
      return (m_firstFree == 0) ? null : m_map[m_firstFree - 1];
    }
docs: Pop a node from the tail of the vector and return the
  top of the stack after the pop.
  
  @return The top of the stack after it's been popped