get_landmarks_from_batch returns an empty list

My code is as follows:

  imgs = imgs.permute(0, 3, 1, 2)# B x C x H x W 
  landmark = self.face_algm.get_landmarks_from_batch(imgs)

The picture I used is the frame intercepted by the MEAD dataset, but it returned an empty list to me, what did I do wrong?