code: def test_empty(self, device):
      B, C, H, W = 1, 1, 32, 32
      PS = 16
      img = torch.rand(B, C, H, W, device=device)
      lafs = torch.zeros(B, 0, 2, 3, device=device)
      sift = SIFTDescriptor(PS).to(device)
      lafsift = LAFDescriptor(sift, PS)
      descs_test = lafsift(img, lafs)
      assert descs_test.shape == (B, 0, 128)
  
imports: import sys
  import pytest
  import torch
  from torch import nn
  from torch.autograd import gradcheck
  import kornia
  import kornia.testing
  from kornia.feature import DescriptorMatcher, GFTTAffNetHardNet, KeyNetHardNet, LAFDescriptor, LocalFeature, ScaleSpaceDetector, SIFTDescriptor, SIFTFeature, extract_patches_from_pyramid, get_laf_center, get_laf_descriptors, get_laf_orientation, get_laf_scale
  from kornia.feature.integrated import LocalFeatureMatcher
  from kornia.geometry import RANSAC, resize, transform_points
  from kornia.testing import assert_close
  from kornia.utils._compat import torch_version_le
label_desc: Use image node_id 2 for calling the TestLAFDescriptor obj's underlying member method code with example usage: obj.test_empty(device) without return types