SSD MobileNet v2 batch size 1 only

I'm trying to use SSD MobileNet v2 320x320

I used exporter_main_v2.py to get saved model.
The generated saved model has hardcoded batch size 1.
Is it the Limitation of SSD models?
Is it possible to save the model with different batch sizes except of 1?

The command I'm running:

# From tensorflow/models/research
export OUTPUT_DIR=./output/ssd_mobilenet_v2_320x320_coco17_tpu-8
python object_detection/exporter_main_v2.py \
    --input_type=image_tensor \
    --pipeline_config_path=ssd_mobilenet_v2_320x320_coco17_tpu-8/pipeline.config \
    --trained_checkpoint_dir=ssd_mobilenet_v2_320x320_coco17_tpu-8/checkpoint \
    --output_directory=$OUTPUT_DIR