def METHOD_NAME(self, param: torch.nn.Parameter) -> Optional[List[int]]:
    """param_used_step
    get the timestep list using the param
    Args:
        param (torch.nn.Parameter): a torch param
    Returns:
        Optional[List[int]]: a list of int indicates the time step of preop hook.
    """
    if param not in self._param_step_dict:
        return None
    else:
        return self._param_step_dict[param]