def _remove_not_ormar_fields(cls, new_kwargs: dict) -> dict:
        """
        Removes primary key for if it's nullable or autoincrement pk field,
        and it's set to None.

        :param new_kwargs: dictionary of model that is about to be saved
        :type new_kwargs: Dict[str, str]
        :return: dictionary of model that is about to be saved
        :rtype: Dict[str, str]
        """
        ormar_fields = {k for k, v in cls.ormar_config.model_fields.items()}
        new_kwargs = {k: v for k, v in new_kwargs.items() if k in ormar_fields}
        return new_kwargs

        Removes primary key for if it's nullable or autoincrement pk field,
        and it's set to None.

        :param new_kwargs: dictionary of model that is about to be saved
        :type new_kwargs: Dict[str, str]
        :return: dictionary of model that is about to be saved
        :rtype: Dict[str, str]
        
ormar/models/mixins/save_mixin.py