<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def unselect(self):
 """ Select a Null bitmasp into this wxDC instance """

        if sys.platform=='win32':
            self.dc.SelectObject(wx.NullBitmap)
            self.IsSelected = False