def __init_subclass__(cls) -> None:
        """Register subclasses as pytree nodes.

        This is necessary to synchronize gradients when using `torch.nn.parallel.DistributedDataParallel` with
        `static_graph=True` with modules that output `ModelOutput` subclasses.
        """
        if is_torch_available():
            _torch_pytree._register_pytree_node(
                cls,
                _model_output_flatten,
                _model_output_unflatten,
            )
Register subclasses as pytree nodes.

        This is necessary to synchronize gradients when using `torch.nn.parallel.DistributedDataParallel` with
        `static_graph=True` with modules that output `ModelOutput` subclasses.
        
dpkd/transformers/src/transformers/utils/generic.py