No test output when running object detection with point pillars

[nikmich1]

Checklist

• [X] I have searched for similar issues.
• [X] I have tested with the latest development wheel.
• [X] I have checked the release documentation and the latest documentation (for master branch).

My Question

Hi, thanks for all the work on this great library! I am following the 'getting started - 3D Object Detection - Running a pretrained model for 3D object detection' part in the Readme.md. I downloaded the KITTI dataset and am using the pointpillars_kitti.yml config file just as in the tutorial. The pipeline.run_test() in the end runs without errors:

https://github.com/isl-org/Open3D-ML/blob/538b661c13dc3ffc7737dbfbcc63cbca0e69508b/README.md?plain=1#L228

However, I don't get any results in the newly created test folder. I already traced the problem back to the save_test_results method, which always receives an empty list as attrs argument for some reason: https://github.com/isl-org/Open3D-ML/blob/538b661c13dc3ffc7737dbfbcc63cbca0e69508b/ml3d/datasets/kitti.py#L234

Could someone kindly point me in the right direction how to fix this, such that files are actually written in the 'save_test_results' method?