Single elem dump
        :param writer:
        :param elem:
        :param container_type:
        :param params:
        :return:

async def _dump_container_val(self, writer, elem, container_type, params=None):
        """
        Single elem dump
        :param writer:
        :param elem:
        :param container_type:
        :param params:
        :return:
        """
        elem_type = container_elem_type(container_type, params)
        await self.dump_field(writer, elem, elem_type, params[1:] if params else None)