message: Drop redundant test
  torch.isnan(None) raises an exception anyway
diff: @@ -46,14 +46,14 @@ def test_dtm_compare_euclidean():
  r6 = dtm.fit_transform(pts2)
  assert r6.detach().numpy() == pytest.approx(r0)
  r6.sum().backward()
  - assert pts2.grad is not None and not torch.isnan(pts2.grad).any()
  + assert not torch.isnan(pts2.grad).any()
  pts2 = torch.tensor(pts, requires_grad=True)
  assert pts2.grad is None
  dtm = DistanceToMeasure(k, implementation="ckdtree", enable_autodiff=True)
  r7 = dtm.fit_transform(pts2)
  assert r7.detach().numpy() == pytest.approx(r0)
  r7.sum().backward()
  - assert pts2.grad is not None and not torch.isnan(pts2.grad).any()
  + assert not torch.isnan(pts2.grad).any()
  def test_dtm_precomputed():
  