Unable to train new baselines while filter_empty = false

Hello there, I've noticed that as soon as I add the following line in my config.py, training crashes:
`dataloader.train.dataset.filter_empty = False`

The line I'm running:
`tools/lazyconfig_train_net.py --config-file configs/new_baselines/mask_rcnn_R_50_FPN_100ep.py`

Logs:
```
[10/24 13:03:50 d2.engine.train_loop]: Starting training from iteration 0
ERROR [10/24 13:03:50 d2.engine.train_loop]: Exception during training:
Traceback (most recent call last):
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/engine/train_loop.py", line 149, in train
self.run_step()
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/engine/train_loop.py", line 409, in run_step
data = next(self._data_loader_iter)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/common.py", line 234, in __iter__
for d in self.dataset:
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 521, in __next__
data = self._next_data()
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 1203, in _next_data
return self._process_data(data)
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 1229, in _process_data
data.reraise()
File "/opt/conda/lib/python3.8/site-packages/torch/_utils.py", line 438, in reraise
raise exception
AttributeError: Caught AttributeError in DataLoader worker process 0.
Original Traceback (most recent call last):
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/_utils/worker.py", line 287, in _worker_loop
data = fetcher.fetch(index)
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/_utils/fetch.py", line 32, in fetch
data.append(next(self.dataset_iter))
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/common.py", line 201, in __iter__
yield self.dataset[idx]
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/common.py", line 90, in __getitem__
data = self._map_func(self._dataset[cur_idx])
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/utils/serialize.py", line 26, in __call__
return self._obj(*args, **kwargs)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/dataset_mapper.py", line 189, in __call__
self._transform_annotations(dataset_dict, transforms, image_shape)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/dataset_mapper.py", line 141, in _transform_annotations
instances.gt_boxes = instances.gt_masks.get_bounding_boxes()
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/structures/instances.py", line 66, in __getattr__
raise AttributeError("Cannot find field '{}' in the given Instances!".format(name))
AttributeError: Cannot find field 'gt_masks' in the given Instances!

[10/24 13:03:50 d2.engine.hooks]: Total training time: 0:00:00 (0:00:00 on hooks)
[10/24 13:03:50 d2.utils.events]:  iter: 0 lr: N/A max_mem: 181M
Traceback (most recent call last):
File "tools/lazyconfig_train_net.py", line 159, in
launch(
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/engine/launch.py", line 82, in launch
main_func(*args)
File "tools/lazyconfig_train_net.py", line 154, in main
do_train(args, cfg)
File "tools/lazyconfig_train_net.py", line 139, in do_train
trainer.train(start_iter, cfg.train.max_iter)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/engine/train_loop.py", line 149, in train
self.run_step()
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/engine/train_loop.py", line 409, in run_step
data = next(self._data_loader_iter)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/common.py", line 234, in __iter__
for d in self.dataset:
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 521, in __next__
data = self._next_data()
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 1203, in _next_data
return self._process_data(data)
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/dataloader.py", line 1229, in _process_data
data.reraise()
File "/opt/conda/lib/python3.8/site-packages/torch/_utils.py", line 438, in reraise
raise exception
AttributeError: Caught AttributeError in DataLoader worker process 0.
Original Traceback (most recent call last):
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/_utils/worker.py", line 287, in _worker_loop
data = fetcher.fetch(index)
File "/opt/conda/lib/python3.8/site-packages/torch/utils/data/_utils/fetch.py", line 32, in fetch
data.append(next(self.dataset_iter))
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/common.py", line 201, in __iter__
yield self.dataset[idx]
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/common.py", line 90, in __getitem__
data = self._map_func(self._dataset[cur_idx])
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/utils/serialize.py", line 26, in __call__
return self._obj(*args, **kwargs)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/dataset_mapper.py", line 189, in __call__
self._transform_annotations(dataset_dict, transforms, image_shape)
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/data/dataset_mapper.py", line 141, in _transform_annotations
instances.gt_boxes = instances.gt_masks.get_bounding_boxes()
File "/home/jovyan/data/kamila/detrex/detectron2/detectron2/structures/instances.py", line 66, in __getattr__
raise AttributeError("Cannot find field '{}' in the given Instances!".format(name))
AttributeError: Cannot find field 'gt_masks' in the given Instances!
```

Environment:
```
2022-10-31 10:18:15 URL:https://raw.githubusercontent.com/facebookresearch/detectron2/main/detectron2/utils/collect_env.py [8391/8391] -> "collect_env.py" [1]
---------------------- -----------------------------------------------------------------------------
sys.platform linux
Python 3.9.12 | packaged by conda-forge | (main, Mar 24 2022, 23:25:59) [GCC 10.3.0]
numpy 1.22.4
detectron2 0.6 @/home/jovyan/data/kamila/detrex/detectron2/detectron2
Compiler GCC 10.3
CUDA compiler not available
DETECTRON2_ENV_MODULE
PyTorch 1.12.1+cu102 @/opt/conda/lib/python3.9/site-packages/torch
PyTorch debug build False
GPU available Yes
GPU 0,1 NVIDIA Quadro RTX 8000 (arch=7.5)
Driver version 465.19.01
CUDA_HOME None - invalid!
Pillow 9.1.1
torchvision 0.13.1+cu102 @/opt/conda/lib/python3.9/site-packages/torchvision
torchvision arch flags /opt/conda/lib/python3.9/site-packages/torchvision/_C.so
fvcore 0.1.5.post20220512
iopath 0.1.9
cv2 4.6.0
---------------------- -----------------------------------------------------------------------------
PyTorch built with:
- GCC 7.3
- C++ Version: 201402
- Intel(R) Math Kernel Library Version 2020.0.0 Product Build 20191122 for Intel(R) 64 architecture applications
- Intel(R) MKL-DNN v2.6.0 (Git Hash 52b5f107dd9cf10910aaa19cb47f3abf9b349815)
- OpenMP 201511 (a.k.a. OpenMP 4.5)
- LAPACK is enabled (usually provided by MKL)
- NNPACK is enabled
- CPU capability usage: AVX2
- CUDA Runtime 10.2
- NVCC architecture flags: -gencode;arch=compute_37,code=sm_37;-gencode;arch=compute_50,code=sm_50;-gencode;arch=compute_60,code=sm_60;-gencode;arch=compute_70,code=sm_70
- CuDNN 7.6.5
- Magma 2.5.2
- Build settings: BLAS_INFO=mkl, BUILD_TYPE=Release, CUDA_VERSION=10.2, CUDNN_VERSION=7.6.5, CXX_COMPILER=/opt/rh/devtoolset-7/root/usr/bin/c++, CXX_FLAGS= -fabi-version=11 -Wno-deprecated -fvisibility-inlines-hidden -DUSE_PTHREADPOOL -fopenmp -DNDEBUG -DUSE_KINETO -DUSE_FBGEMM -DUSE_QNNPACK -DUSE_PYTORCH_QNNPACK -DUSE_XNNPACK -DSYMBOLICATE_MOBILE_DEBUG_HANDLE -DEDGE_PROFILER_USE_KINETO -O2 -fPIC -Wno-narrowing -Wall -Wextra -Werror=return-type -Wno-missing-field-initializers -Wno-type-limits -Wno-array-bounds -Wno-unknown-pragmas -Wno-unused-parameter -Wno-unused-function -Wno-unused-result -Wno-unused-local-typedefs -Wno-strict-overflow -Wno-strict-aliasing -Wno-error=deprecated-declarations -Wno-stringop-overflow -Wno-psabi -Wno-error=pedantic -Wno-error=redundant-decls -Wno-error=old-style-cast -fdiagnostics-color=always -faligned-new -Wno-unused-but-set-variable -Wno-maybe-uninitialized -fno-math-errno -fno-trapping-math -Werror=format -Wno-stringop-overflow, LAPACK_INFO=mkl, PERF_WITH_AVX=1, PERF_WITH_AVX2=1, PERF_WITH_AVX512=1, TORCH_VERSION=1.12.1, USE_CUDA=ON, USE_CUDNN=ON, USE_EXCEPTION_PTR=1, USE_GFLAGS=OFF, USE_GLOG=OFF, USE_MKL=ON, USE_MKLDNN=OFF, USE_MPI=OFF, USE_NCCL=ON, USE_NNPACK=ON, USE_OPENMP=ON, USE_ROCM=OFF,

Testing NCCL connectivity ... this should not hang.
NCCL succeeded.
```

Start with tools/lazyconfig_train_net.py and trace the failing data path through detectron2/data/common.py into detectron2/data/dataset_mapper.py, especially _transform_annotations at the reported line. Reproduce with configs/new_baselines/mask_rcnn_R_50_FPN_100ep.py after setting dataloader.train.dataset.filter_empty = False, then verify training passes iteration 0 without the missing gt_masks error.

Written by the indexing model from the issue text.