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