docstr: Test corner case where a network might predict no boxes and no
  gt.
code: def test_center_region_assigner_with_empty_boxes_and_gt(self):
      """Test corner case where a network might predict no boxes and no
      gt."""
      center_region_assigner = CenterRegionAssigner(
          pos_scale=0.2, neg_scale=0.2, min_pos_iof=0.01
      )
      priors = torch.empty((0, 4))
      gt_bboxes = torch.empty((0, 4))
      gt_labels = torch.empty(0)
  
      pred_instances = InstanceData(priors=priors)
      gt_instances = InstanceData(bboxes=gt_bboxes, labels=gt_labels)
      assign_result = center_region_assigner.assign(
          pred_instances, gt_instances
      )
      self.assertEqual(len(assign_result.gt_inds), 0)
  
file_path: mmdetection/tests/test_models/test_task_modules/test_assigners/test_center_region_assigner.py
imports: from unittest import TestCase
  import torch
  from mmengine.structures import InstanceData
  from mmdet.models.task_modules.assigners import CenterRegionAssigner
label_desc: Use image node_id 6 for calling the TestCenterRegionAssigner obj's underlying member method code with example usage: obj.test_center_region_assigner_with_empty_boxes_and_gt() without return types