models/research/object_detection/exporter_main_v2.py give me error "ImportError: cannot import name 'builder'"

On my jetson nano : when using models/research/object_detection/exporter_main_v2.py i got the error "ImportError: cannot import name 'builder'

It was working great 1-2 years ago ... :-( but when I try to git clone the tag v2.6.0, there is no research directory ... it contains only Official and Orbit directory ...

how can i do for git clone the repo from tag 2.6.0 with the research directory inside ??

Can someone help me ?

Thanks !

git clone --recursive https://github.com/tensorflow/models.git

cd models/research
protoc object_detection/protos/*.proto --python_out=.
cp object_detection/packages/tf2/setup.py .
python3 -m pip install .

cd ../..

wget http://download.tensorflow.org/models/object_detection/tf2/20200711/ssd_mobilenet_v2_fpnlite_320x320_coco17_tpu-8.tar.gz
tar -zxf ssd_mobilenet_v2_fpnlite_320x320_coco17_tpu-8.tar.gz
rm ssd_mobilenet_v2_fpnlite_320x320_coco17_tpu-8.tar.gz

set_env PYTHONPATH="/env/python:/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models/research:/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models/research/slim:/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models"

mkdir tfmodel_ssd_mobilenet_v2_320x320_coco17_tpu-8

pip3 install tf_slim

sudo cp -r models/official /usr/local/lib/python3.6/dist-packages

python3 models/research/object_detection/exporter_main_v2.py --input_type float_image_tensor --trained_checkpoint_dir ssd_mobilenet_v2_fpnlite_320x320_coco17_tpu-8/checkpoint/ --pipeline_config_path ssd_mobilenet_v2_fpnlite_320x320_coco17_tpu-8/pipeline.config --output_directory tfmodel_ssd_mobilenet_v2_320x320_coco17_tpu-8

I got the error :

Traceback (most recent call last):
  File "models/research/object_detection/exporter_main_v2.py", line 104, in <module>
    from object_detection import exporter_lib_v2
  File "/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models/research/object_detection/exporter_lib_v2.py", line 21, in <module>
    from object_detection.builders import model_builder
  File "/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models/research/object_detection/builders/model_builder.py", line 23, in <module>
    from object_detection.builders import anchor_generator_builder
  File "/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models/research/object_detection/builders/anchor_generator_builder.py", line 26, in <module>
    from object_detection.protos import anchor_generator_pb2
  File "/home/jetson/notebook/Jetbot/6. Détection et suivi d'objet/models/research/object_detection/protos/anchor_generator_pb2.py", line 5, in <module>
    from google.protobuf.internal import builder as _builder
ImportError: cannot import name 'builder'