def _preprocess_params(cls, kwargs):
        """Returns a preprocessed dictionary of parameters.
        Use this to filter the kwargs passed to `new`, `create`,
        `build` methods.

        Args:

            **kwargs: a dictionary of parameters
        """
        # kwargs.pop('csrf_token', None)
        for attr, val in kwargs.items():
            if cls.is_the_primary_key(attr) and cls._prevent_primary_key_initialization_:
                del kwargs[attr]
                continue
            if val == "":
                # Making an assumption that there is no good usecase
                # for setting an empty string. This will help prevent
                # cases where empty string is sent because of client
                # not clearing form fields to null
                kwargs[attr] = None
                continue
            if attr in class_mapper(cls).relationships and attr not in cls._no_overwrite_:
                rel = class_mapper(cls).relationships[attr]
                if rel.uselist:
                    if isinstance(val, list):
                        if all(isinstance(v, dict) for v in val):
                            rel_cls = cls.mapped_rel_class(attr)
                            kwargs[attr] = rel_cls.update_or_new_all(
                                list_of_kwargs=val, keys=[rel_cls.primary_key_name()])
                    elif isinstance(val, dict):
                        rel_cls = cls.mapped_rel_class(attr)
                        mapping_col = rel.collection_class().keyfunc.name
                        list_of_kwargs = [merge(v, {mapping_col: k}) for k, v in val.items()]
                        kwargs[attr] = {getattr(obj, mapping_col): obj for obj in rel_cls.update_or_new_all(
                            list_of_kwargs=list_of_kwargs, keys=[rel_cls.primary_key_name()])}
                elif isinstance(val, dict):
                    rel_cls = cls.mapped_rel_class(attr)
                    kwargs[attr] = rel_cls.update_or_new(
                        **merge(val, {'keys': [rel_cls.primary_key_name()]}))
        return kwargs