depth supervision code in maptrv2 is not valid? code bug?

[lwx422]

maptrv2 branch, file: projects/mmdet3d_plugin/maptr/modules/encoder.py
line 1162--1164 code:
fg_mask = depth_labels > 0.0 # 只计算有深度的前景的深度loss
depth_labels = depth_labels[fg_mask]
depth_preds = depth_preds[fg_mask]`
the "fg_mask" only keep positive samples, all negative samples are filtered which make this branch invalid, please check.