code: public final String pop()
    {
  
      if (m_firstFree <= 0)
        return null;
  
      m_firstFree--;
  
      String s = m_map[m_firstFree];
  
      m_map[m_firstFree] = null;
  
      return s;
    }
docs: Pop the tail of this vector.
  
  @return The String last added to this vector or null not found.
  The string is removed from the vector.