"Params must be subclasses of Param"
        )
        loc: tuple[str, ...] = (field_info.in_.value,)
        v_, errors_ = _validate_value_with_model_field(
            field=first_field, value=params_to_process, values=values, loc=loc
        )
        return {first_field.name: v_}, errors_

    for field in fields:
        value = _get_multidict_value(field, received_params)
        field_info = field.field_info