'autoscale only None-valued vmin or vmax'

def autoscale_None(self, A):

    if ((self.vmin is not None) and (self.vmax is not None)):
        pass
    if (self.vmin is None):
        self.vmin = np.ma.min(A)
    if (self.vmax is None):
        self.vmax = np.ma.max(A)
    self._transform_vmin_vmax()
