DeepSpeed

ddd35718 - Add default value to "checkpoint_folder" in "load_state_dict" of bf16_optimizer (#6446)

Add default value to "checkpoint_folder" in "load_state_dict" of bf16_optimizer (#6446) Add default value `checkpoint_folder=None` for compatibility. Co-authored-by: Olatunji Ruwase <olruwase@microsoft.com>